FIX: compilation failure when using XCode

src/include/reb-c.h

@@ -249,6 +249,11 @@ typedef void(*CFUNC)(void *);
 **
 ***********************************************************************/
 
+#ifdef __has_builtin
+# define HAS_BUILTIN(x) __has_builtin(x)
+#else
+# define HAS_BUILTIN(x) 0
+#endif
 
 #if defined(_MSC_VER)
 # define FORCE_INLINE __forceinline
@@ -259,16 +264,21 @@ typedef void(*CFUNC)(void *);
 // Other compilers..
 #else // defined(_MSC_VER)
 # define FORCE_INLINE inline __attribute__((always_inline))
-inline uint32_t rotl32(uint32_t x, int8_t r)
-{
- return (x << r) | (x >> (32 - r));
-}
-inline uint64_t rotl64(uint64_t x, int8_t r)
-{
- return (x << r) | (x >> (64 - r));
-}
-# define ROTL32(x,y) rotl32(x,y)
-# define ROTL64(x,y) rotl64(x,y)
+# if HAS_BUILTIN(__builtin_rotateleft32) && HAS_BUILTIN(__builtin_rotateleft64)
+# define ROTL32(x,y) __builtin_rotateleft32(x,y)
+# define ROTL64(x,y) __builtin_rotateleft64(x,y)
+# else
+ FORCE_INLINE uint32_t rotl32(uint32_t x, int8_t r)
+ {
+ return (x << r) | (x >> (32 - r));
+ }
+ FORCE_INLINE uint64_t rotl64(uint64_t x, int8_t r)
+ {
+ return (x << r) | (x >> (64 - r));
+ }
+# define ROTL32(x,y) rotl32(x,y)
+# define ROTL64(x,y) rotl64(x,y)
+# endif
 # define BIG_CONSTANT(x) (x##LLU)
 #endif // !defined(_MSC_VER)