Move down __has_builtin to fix GCC builds

Author: dennisameling

compat/bswap.h

@@ -35,12 +35,7 @@ static inline uint64_t default_bswap64(uint64_t val)
 #undef bswap32
 #undef bswap64
 
-#if defined(__has_builtin) && __has_builtin(__builtin_bswap64)
-
-#define bswap32(x)     __builtin_bswap32((x))
-#define bswap64(x)     __builtin_bswap64((x))
-
-#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
 
 #define bswap32 git_bswap32
 static inline uint32_t git_bswap32(uint32_t x)
@@ -79,6 +74,11 @@ static inline uint64_t git_bswap64(uint64_t x)
 }
 #endif
 
+#elif defined(__has_builtin) && __has_builtin(__builtin_bswap64) /* for clang arm64; gcc only added this in gcc 10 */
+
+#define bswap32(x)     __builtin_bswap32((x))
+#define bswap64(x)     __builtin_bswap64((x))
+
 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM64))
 
 #include <stdlib.h>