Move __has_builtin() fallback define to compiler.h

lib/common/compiler.h

@@ -196,6 +196,11 @@
     #define STATIC_BMI2 0
 #endif
 
+/* compat. with non-clang compilers */
+#ifndef __has_builtin
+#  define __has_builtin(x) 0
+#endif
+
 /* detects whether we are being compiled under msan */
 #if defined (__has_feature)
 #  if __has_feature(memory_sanitizer)

lib/common/mem.h

@@ -39,10 +39,6 @@ extern "C" {
 #  define MEM_STATIC static  /* this version may generate warnings for unused static functions; disable the relevant warning */
 #endif
 
-#ifndef __has_builtin
-#  define __has_builtin(x) 0  /* compat. with non-clang compilers */
-#endif
-
 /* code only tested on 32 and 64 bits systems */
 MEM_STATIC void MEM_check(void) { DEBUG_STATIC_ASSERT((sizeof(size_t)==4) || (sizeof(size_t)==8)); }