Fix always_inline warning in gcc

The always_inline attribute does not imply C99 inline in some
versions of GCC.

See also https://bugzilla.mozilla.org/show_bug.cgi?id=697810

Author: zhihaoy

sleef/src/common/misc.h

@@ -257,7 +257,7 @@ typedef union {
 #else
 #define CONST
 #endif
-#define INLINE __attribute__((always_inline))
+#define INLINE __attribute__((always_inline)) inline
 
 #if defined(__MINGW32__) || defined(__MINGW64__) || defined(__CYGWIN__)
 #ifndef SLEEF_STATIC_LIBS