Avoid redefining inline

System headers (e.g. gutils.h) may define 'inline', #undefine it
before #defining.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

osdep.h

@@ -70,10 +70,12 @@ typedef signed int              int_fast16_t;
 #ifndef always_inline
 #if !((__GNUC__ < 3) || defined(__APPLE__))
 #ifdef __OPTIMIZE__
+#undef inline
 #define inline __attribute__ (( always_inline )) __inline__
 #endif
 #endif
 #else
+#undef inline
 #define inline always_inline
 #endif