extern-inline: do not always suppress extern inline on OS X

* m4/extern-inline.m4 (gl_EXTERN_INLINE): Suppress the use of
extern inline on Apple only if the particular compile-time
configuration is known to have the problem.
(_GL_EXTERN_INLINE_APPLE_BUG): New private macro, to implement this.
(_GL_EXTERN_LNLINE_IN_USE): New macro, intended for use by
other Gnulib modules.

ChangeLog

 2013-09-19  Paul Eggert  <eggert@cs.ucla.edu>
 
+	extern-inline: do not always suppress extern inline on OS X
+	* m4/extern-inline.m4 (gl_EXTERN_INLINE): Suppress the use of
+	extern inline on Apple only if the particular compile-time
+	configuration is known to have the problem.
+	(_GL_EXTERN_INLINE_APPLE_BUG): New private macro, to implement this.
+	(_GL_EXTERN_LNLINE_IN_USE): New macro, intended for use by
+	other Gnulib modules.
+
 	extern-inline: document fixes for ctype and wctype macros
 	* doc/posix-functions/isalnum.texi, doc/posix-functions/isalpha.texi:
 	* doc/posix-functions/isascii.texi, doc/posix-functions/isblank.texi:

m4/extern-inline.m4

@@ -19,20 +19,28 @@ AC_DEFUN([gl_EXTERN_INLINE],
    'reference to static identifier "f" in extern inline function'.
    This bug was observed with Sun C 5.12 SunOS_i386 2011/11/16.
 
-   Suppress the use of extern inline on Apple's platforms, as Libc at least
-   through Libc-825.26 (2013-04-09) is incompatible with it; see, e.g.,
+   Suppress the use of extern inline on problematic Apple configurations, as
+   Libc at least through Libc-825.26 (2013-04-09) mishandles it; see, e.g.,
    <http://lists.gnu.org/archive/html/bug-gnulib/2012-12/msg00023.html>.
    Perhaps Apple will fix this some day.  */
+#if (defined __APPLE__ \
+     && ((! defined _DONT_USE_CTYPE_INLINE_ \
+          && (defined __GNUC__ || defined __cplusplus)) \
+         || (defined _FORTIFY_SOURCE && 0 < _FORTIFY_SOURCE \
+             && defined __GNUC__ && ! defined __cplusplus)))
+# define _GL_EXTERN_INLINE_APPLE_BUG
+#endif
 #if ((__GNUC__ \
       ? defined __GNUC_STDC_INLINE__ && __GNUC_STDC_INLINE__ \
       : (199901L <= __STDC_VERSION__ \
          && !defined __HP_cc \
          && !(defined __SUNPRO_C && __STDC__))) \
-     && !defined __APPLE__)
+     && !defined _GL_EXTERN_INLINE_APPLE_BUG)
 # define _GL_INLINE inline
 # define _GL_EXTERN_INLINE extern inline
+# define _GL_EXTERN_INLINE_IN_USE
 #elif (2 < __GNUC__ + (7 <= __GNUC_MINOR__) && !defined __STRICT_ANSI__ \
-       && !defined __APPLE__)
+       && !defined _GL_EXTERN_INLINE_APPLE_BUG)
 # if __GNUC_GNU_INLINE__
    /* __gnu_inline__ suppresses a GCC 4.2 diagnostic.  */
 #  define _GL_INLINE extern inline __attribute__ ((__gnu_inline__))
@@ -40,6 +48,7 @@ AC_DEFUN([gl_EXTERN_INLINE],
 #  define _GL_INLINE extern inline
 # endif
 # define _GL_EXTERN_INLINE extern
+# define _GL_EXTERN_INLINE_IN_USE
 #else
 # define _GL_INLINE static _GL_UNUSED
 # define _GL_EXTERN_INLINE static _GL_UNUSED