gallium: add ALWAYS_INLINE

Used when we want to be sure the compiler inlines a large function into
an inner loop.

src/gallium/include/pipe/p_compiler.h

@@ -102,6 +102,16 @@ typedef unsigned char boolean;
 #  endif
 #endif
 
+/* Forced function inlining */
+#ifndef ALWAYS_INLINE
+#  ifdef __GNUC__
+#    define ALWAYS_INLINE inline __attribute__((always_inline))
+#  elif defined(_MSC_VER)
+#    define ALWAYS_INLINE __forceinline
+#  else
+#    define ALWAYS_INLINE INLINE
+#  endif
+#endif
 
 /* Function visibility */
 #ifndef PUBLIC