Without this change, a project that defines warning(x) or unused as a
macro for its own use before including <curl/curl.h> can get warnings
like this:

 /usr/include/curl/typecheck-gcc.h:147:1: error: expected ‘)’ before ‘(’ token
 /usr/include/curl/typecheck-gcc.h:147:1: error: expected identifier or ‘(’ before ‘)’ token
 /usr/include/curl/typecheck-gcc.h:149:1: error: expected ‘)’ before ‘(’ token
 ...

GCC has supported the attribute names with surrounding __ since
1994 (r8412, "Check for attributes with leading and trailing double
underscores"), so this shouldn't hurt portability.

---
Based on a true story.  Thoughts?
Thanks for keeping curl working nicely.
Sincerely,
Jonathan
 include/curl/typecheck-gcc.h |    5 +++--
 lib/setup.h                  |    2 +-
 m4/curl-compilers.m4         |    6 +++---
 3 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/curl/typecheck-gcc.h b/include/curl/typecheck-gcc.h
index 5c584b00..6f81f69e 100644
--- a/include/curl/typecheck-gcc.h
+++ b/include/curl/typecheck-gcc.h
@@ -141,8 +141,9 @@ __extension__ ({                                                              \
 
 /* To define a new warning, use _CURL_WARNING(identifier, "message") */
 #define _CURL_WARNING(id, message)                                            \
-  static void __attribute__((warning(message))) __attribute__((unused))       \
-  __attribute__((noinline)) id(void) { __asm__(""); }
+  static void __attribute__((__warning__(message)))                           \
+  __attribute__((__unused__)) __attribute__((__noinline__)) id(void)          \
+  { __asm__(""); }
 
 _CURL_WARNING(_curl_easy_setopt_err_long,
   "curl_easy_setopt expects a long argument for this option")
diff --git a/lib/setup.h b/lib/setup.h
index 6ce93db4..4bce5a93 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -611,7 +611,7 @@ int netware_init(void);
 #ifndef __GNUC__
 #define UNUSED_PARAM /*NOTHING*/
 #else
-#define UNUSED_PARAM __attribute__((unused))
+#define UNUSED_PARAM __attribute__((__unused__))
 #endif
 
 /*
diff --git a/m4/curl-compilers.m4 b/m4/curl-compilers.m4
index 9b212e46..2de33d55 100644
--- a/m4/curl-compilers.m4
+++ b/m4/curl-compilers.m4
@@ -1393,7 +1393,7 @@ AC_DEFUN([CURL_CHECK_COMPILER_SYMBOL_HIDING], [
   case "$compiler_id" in
     CLANG)
       dnl All versions of clang support -fvisibility=
-      tmp_EXTERN="__attribute__ ((visibility (\"default\")))"
+      tmp_EXTERN="__attribute__ ((__visibility__ (\"default\")))"
       tmp_CFLAGS="-fvisibility=hidden"
       supports_symbol_hiding="yes"
       ;;
@@ -1401,7 +1401,7 @@ AC_DEFUN([CURL_CHECK_COMPILER_SYMBOL_HIDING], [
       dnl Only gcc 3.4 or later
       if test "$compiler_num" -ge "304"; then
         if $CC --help --verbose 2>&1 | grep fvisibility= > /dev/null ; then
-          tmp_EXTERN="__attribute__ ((visibility (\"default\")))"
+          tmp_EXTERN="__attribute__ ((__visibility__ (\"default\")))"
           tmp_CFLAGS="-fvisibility=hidden"
           supports_symbol_hiding="yes"
         fi
@@ -1420,7 +1420,7 @@ AC_DEFUN([CURL_CHECK_COMPILER_SYMBOL_HIDING], [
               printf("icc fvisibility bug test");
             ]])
           ],[
-            tmp_EXTERN="__attribute__ ((visibility (\"default\")))"
+            tmp_EXTERN="__attribute__ ((__visibility__ (\"default\")))"
             tmp_CFLAGS="-fvisibility=hidden"
             supports_symbol_hiding="yes"
           ])
-- 
1.7.10
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