includes: Replace QEMU_GNUC_PREREQ with "__has_builtin || !defined(__clang__)"

Since we require GCC version 4.8 or newer now, we can be sure that
the builtin functions are always available on GCC. And for Clang,
we can check the availablility with __has_builtin instead.
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NThomas Huth <thuth@redhat.com>

include/qemu/compiler.h

@@ -127,7 +127,7 @@
 #define __has_builtin(x) 0 /* compatibility with non-clang compilers */
 #endif
 
-#if __has_builtin(__builtin_assume_aligned) || QEMU_GNUC_PREREQ(4, 7)
+#if __has_builtin(__builtin_assume_aligned) || !defined(__clang__)
 #define HAS_ASSUME_ALIGNED
 #endif
 

include/qemu/host-utils.h

@@ -207,7 +207,7 @@ static inline int cto64(uint64_t val)
  */
 static inline int clrsb32(uint32_t val)
 {
-#if QEMU_GNUC_PREREQ(4, 7)
+#if __has_builtin(__builtin_clrsb) || !defined(__clang__)
     return __builtin_clrsb(val);
 #else
     return clz32(val ^ ((int32_t)val >> 1)) - 1;
@@ -223,7 +223,7 @@ static inline int clrsb32(uint32_t val)
  */
 static inline int clrsb64(uint64_t val)
 {
-#if QEMU_GNUC_PREREQ(4, 7)
+#if __has_builtin(__builtin_clrsbll) || !defined(__clang__)
     return __builtin_clrsbll(val);
 #else
     return clz64(val ^ ((int64_t)val >> 1)) - 1;