+ It defines a macro __GNUC_GNU_INLINE__ to indicate this situation.
+
+ Whereas Apple GCC 4.0.1 build 5479 without -std=c99 or -std=gnu99
+ implements the GNU C inline semantics and defines the macro
+ __GNUC_GNU_INLINE__, but it does not warn and does not support
+ __attribute__ ((__gnu_inline__)).
+
+ All in all, these are the possible combinations. For every compiler,
+ we need to choose ARGP_FS_EI so that the corresponding table cell
+ contains an "ok".
+
+ \ ARGP_FS_EI inline extern extern
+ \ inline inline
+ CC \ __attribute__
+ ((gnu_inline))
+
+ gcc 4.3.0 error ok ok
+ gcc 4.3.0 -std=gnu99 -fgnu89-inline error ok ok
+ gcc 4.3.0 -std=gnu99 ok error ok
+
+ gcc 4.2.2 error ok ok
+ gcc 4.2.2 -std=gnu99 -fgnu89-inline error ok ok
+ gcc 4.2.2 -std=gnu99 error warning ok
+
+ gcc 4.1.2 error ok warning
+ gcc 4.1.2 -std=gnu99 error ok warning
+
+ Apple gcc 4.0.1 error ok warning
+ Apple gcc 4.0.1 -std=gnu99 ok error warning
+ */