Stop dynamically generating `libcurl.def` with the next curl release,
which provides it and uses it automatically in GNU Make builds.

curl/curl@2ebc74c
curl/curl#11546

2ebc74c curl#11546 introduced sharing
libcurl objects for shared and static targets.

The above automatically enabled for Windows builds, with an option to
disable with `SHARE_LIB_OBJECT=OFF`.

This patch extend this feature for all platforms as a manual option.
You can enable it by setting `SHARE_LIB_OBJECT=ON`. Shared objects will
be built in PIC mode, meaning the static lib will also have PIC code.

EXPERIMENTAL.

Closes #xxxxx

2ebc74c #11546 introduced sharing
libcurl objects for shared and static targets.

The above automatically enabled for Windows builds, with an option to
disable with `SHARE_LIB_OBJECT=OFF`.

This patch extend this feature to all platforms as a manual option.
You can enable it by setting `SHARE_LIB_OBJECT=ON`. Then shared objects
are built in PIC mode, meaning the static lib will also have PIC code.

[EXPERIMENTAL]

Closes #11627

Before this patch CMake builds used two separate compilation passes to
build the shared and static libcurl respectively. This patch allows to
reduce that to a single pass if the target platform and build settings
allow it.

This reduces CMake build times when building both static and shared
libcurl at the same time, making these dual builds an almost zero-cost
option.

Enable this feature for Windows builds, where the difference between the
two passes was the use of `__declspec(dllexport)` attribute for exported
API functions for the shared builds. This patch replaces this method
with the use of `libcurl.def` at DLL link time.

Also update `Makefile.mk` to use `libcurl.def` to export libcurl API
symbols on Windows. This simplifies (or fixes) this build method (e.g.
in curl-for-win, which generated a `libcurl.def` from `.h` files using
an elaborate set of transformations).

`libcurl.def` has the maintenance cost of keeping the list of public
libcurl API symbols up-to-date. This list seldom changes, so the cost
is low.

Closes curl#11546

2ebc74c curl#11546 introduced sharing
libcurl objects for shared and static targets.

The above automatically enabled for Windows builds, with an option to
disable with `SHARE_LIB_OBJECT=OFF`.

This patch extend this feature to all platforms as a manual option.
You can enable it by setting `SHARE_LIB_OBJECT=ON`. Then shared objects
are built in PIC mode, meaning the static lib will also have PIC code.

[EXPERIMENTAL]

Closes curl#11627

Switch from `curl-gnumake.sh` to `curl-cmake.sh` with upcoming curl
release v8.5.0.

cmake builds are now _faster_ for Windows builds than raw gnumake
(aka `Makefile.mk`). They also use 'unity' mode, which makes builds
run fast with the side-effect of also creating potentially more
efficient binaries by allowing better compiler optimizations.

This also makes curl-for-win use the same build system for all target
platforms (`Makefile.mk` is not available for *nix platforms).

Initially on 2022-07-04 cmake was 25% slower than gnumake. By
2022-09-26 this reduced to 20%, by 2023-07-29 to 18% and after the
latest round of updates gnumake came out 7% slower than cmake.
This is for Windows, for a triple x64, arm64 and x86 build. In
absolute times this is 27m22s for cmake and 29m11s for gnumake.

(FWIW autotools builds are 52% slower than cmake unity builds now.)

Making cmake builds fast was a multi-year effort with these major steps:

1. add support for cmake builds in curl-for-win.
   420e73c
2. bring it in-line with gnumake and autotools builds and tidy-up
   as much as possible. Scattered to a many commits.
3. delete a whole bunch of unused feature detections.
   curl/curl@4d73854
   curl/curl#9044
   (and a lot more smaller commits)
4. speed up picky warning option initialization by avoiding brute-force
   all options. (first in libssh2, then in curl, then applied also
   ngtcp2, nghttp3, nghttp2)
   curl/curl@9c543de
   curl/curl#10973
5. implement single build run for shared and static libcurl + tool
   (first in libssh2)
   curl/curl@1199308
   curl/curl#11505
   53dcd49
6. implement single build pass for shared and static libcurl
   (for Windows initially)
   curl/curl@2ebc74c
   curl/curl#11546
7. extend above to non-Windows (e.g. macOS)
   curl/curl@fc9bfb1
   curl/curl#11627
   bafa77d (mac)
   1b27304 (linux)
8. implement unity builds: single compiler invocation for libcurl + tool
   curl/curl@3f8fc25
   curl/curl#11095
   curl/curl@f42a279
   curl/curl#11928
   67d7fd3
9. speed up 4x the cmake initialization phase (for Windows)
   curl/curl@2100d9f
   curl/curl#12044
10. speed up cmake initialization even more by pre-filling
   detection results for our well-known mingw-w64 environments.
   74dd967
   5a43c61

+1: speed up autotools initialization by mitigating a brute-force
   feature detection on Windows. This reduced total build times
   by 5 minutes at the time, for the 3 Windows targets in total.
   curl/curl@6adcff6
   curl/curl#9591

Also update build times for cmake-unity and gnumake, based on runs:
cmake-unity: https://ci.appveyor.com/project/curlorg/curl-for-win/builds/48357875
gnumake: https://ci.appveyor.com/project/curlorg/curl-for-win/builds/48358005

- 898b012 curl#1288
- 5de6848 curl#10023
- bunch of others that are completed
- `NTLM_WB_ENABLED` is implemented in a basic form, and now also
  scheduled for removal, so a TODO at this point isn't useful.

And this 'to-check' item:

Q: "The cmake build selected to run gcc with -fPIC on my box while the
   plain configure script did not."

A: With CMake, since 2ebc74c curl#11546
   and fc9bfb1 curl#11627, we explicitly
   enable PIC for libcurl shared lib. Or when building libcurl for
   shared and static lib in a single pass. We do this by default for
   Windows or when enabled by the user via `SHARE_LIB_OBJECT`.
   Otherwise we don't touch this setting. Meaning the default set by
   CMake (if any) or the toolchain is used. On Debian Bookworm, this
   means that PIC is disabled for static libs by default. Some platforms
   (like macOS), has PIC enabled by default.
   autotools supports the double-pass mode only, and in that case
   CMake seems to match PIC behaviour now (as tested on Linux with gcc.)

Closes #xxxxx

- 898b012 curl#1288
- 5de6848 curl#10023
- bunch of others that are completed
- `NTLM_WB_ENABLED` is implemented in a basic form, and now also
  scheduled for removal, so a TODO at this point isn't useful.

And this 'to-check' item:

Q: "The cmake build selected to run gcc with -fPIC on my box while the
   plain configure script did not."

A: With CMake, since 2ebc74c curl#11546
   and fc9bfb1 curl#11627, we explicitly
   enable PIC for libcurl shared lib. Or when building libcurl for
   shared and static lib in a single pass. We do this by default for
   Windows or when enabled by the user via `SHARE_LIB_OBJECT`.
   Otherwise we don't touch this setting. Meaning the default set by
   CMake (if any) or the toolchain is used. On Debian Bookworm, this
   means that PIC is disabled for static libs by default. Some platforms
   (like macOS), has PIC enabled by default.
   autotools supports the double-pass mode only, and in that case
   CMake seems to match PIC behaviour now (as tested on Linux with gcc.)

Follow-up to 5d5dfdb curl#12500

Closes #xxxxx

- manual completed: 898b012 #1288
- soname completed: 5de6848 #10023
- bunch of others that are completed
- `NTLM_WB_ENABLED` is implemented in a basic form, and now also
  scheduled for removal, so a TODO at this point isn't useful.

And this 'to-check' item:

Q: "The cmake build selected to run gcc with -fPIC on my box while the
   plain configure script did not."

A: With CMake, since 2ebc74c #11546
   and fc9bfb1 #11627, we explicitly
   enable PIC for libcurl shared lib. Or when building libcurl for
   shared and static lib in a single pass. We do this by default for
   Windows or when enabled by the user via `SHARE_LIB_OBJECT`.
   Otherwise we don't touch this setting. Meaning the default set by
   CMake (if any) or the toolchain is used. On Debian Bookworm, this
   means that PIC is disabled for static libs by default. Some platforms
   (like macOS), has PIC enabled by default.
   autotools supports the double-pass mode only, and in that case
   CMake seems to match PIC behaviour now (as tested on Linux with gcc.)

Follow-up to 5d5dfdb #12500

Reviewed-by: Jay Satiro
Closes #12509