```
lib/rand.c:151:7: error: code will never be executed [-Werror,-Wunreachable-code]
  if(!seeded) {
      ^~~~~~
```
Ref: https://github.com/curl/curl/actions/runs/6880886309/job/18716044703?pr=12331#step:7:72

Including fixing these fallouts:
https://github.com/curl/curl/actions/runs/6883016087/job/18722707368?pr=12331#step:7:109

Follow-up to 033f8e2 curl#12324

The warning is triggered by libtool-generate code on MSYS gcc env:
```
bash.exe : ./.libs/lt-curl.c: In function 'lt_fatal':
At line:88 char:3
+   & bash -e -c "cd $env:POSIX_PATH_PREFIX/c/projects/curl && autoreco ...
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (./.libs/lt-curl...ion 'lt_fatal'::String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

./.libs/lt-curl.c:594:1: warning: function might be candidate for attribute 'noreturn' [-Wsuggest-attribute=noreturn]
  594 | lt_fatal (const char *file, int line, const char *message, ...)
      | ^~~~~~~~
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/48553586/job/3qkgjauiqla5fj45?fullLog=true#L1675

It might need to be applied also to clang and possible to other target
environments where this pops up in the future.

https://github.com/curl/curl/actions/runs/6882803986/job/18722082562?pr=12331#step:33:1870

```
vtls/sectransp.c:3448:9: error: 'break' will never be executed [-Werror,-Wunreachable-code-break]
        break;
        ^~~~~
vtls/sectransp.c:3428:9: error: 'break' will never be executed [-Werror,-Wunreachable-code-break]
        break;
        ^~~~~
vtls/sectransp.c:3418:9: error: 'break' will never be executed [-Werror,-Wunreachable-code-break]
        break;
        ^~~~~
```
Ref: https://github.com/curl/curl/actions/runs/6891484996/job/18746659406?pr=12331#step:9:1193

These were detected in `else` branches of dynamic feature checks,
where the results of these checks is known at compiler-time, e.g.

```
if(SecCertificateCopySubjectSummary)  /* -> true */
```

Probably fixable as a separate micro-project, but given that
SecureTransport is a deprecated API anyway, for now I just silence
these warnings for the whole SecureTransport code.

```
vtls/sectransp.c:985:9: error: code will never be executed [-Werror,-Wunreachable-code]
  (void)SecCertificateCopyCommonName(cert, &server_cert_summary);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
vtls/sectransp.c:980:6: error: code will never be executed [-Werror,-Wunreachable-code]
  if(SecCertificateCopySubjectSummary)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
vtls/sectransp.c:1408:14: error: code will never be executed [-Werror,-Wunreachable-code]
[...]
long i = ssl_version;
             ^~~~~~~~~~~
vtls/sectransp.c:1743:11: error: code will never be executed [-Werror,-Wunreachable-code]
    (void)SSLSetProtocolVersionEnabled(backend->ssl_ctx,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
vtls/sectransp.c:1683:8: error: code will never be executed [-Werror,-Wunreachable-code]
[...]
if(backend->ssl_ctx)
       ^~~~~~~
vtls/sectransp.c:2969:11: error: code will never be executed [-Werror,-Wunreachable-code]
    err = SSLCopyPeerCertificates(backend->ssl_ctx, &server_certs);
          ^~~~~~~~~~~~~~~~~~~~~~~
vtls/sectransp.c:3171:13: error: code will never be executed [-Werror,-Wunreachable-code]
      (void)SSLDisposeContext(backend->ssl_ctx);
            ^~~~~~~~~~~~~~~~~
```
Ref: https://github.com/curl/curl/actions/runs/6891484996/job/18746659406?pr=12331#step:9:1168

Present since initial commit ae1912c
(1999-12-29). This suggests this may not be needed anymore, but if
it does, we may restore this for those specific (non-Windows) systems.

Originally added in 687df5c (2010-08-02).
This got complicated later: c49e968

If there are still systems around where this is causing warnings,
we may restore the prototype, but for those specific systems only.
Otherwise it's a double declaration on every other system which we
must match precisely, and may also cause a warning.

…sVistaOrGreater`

in unity builds.