[PATCH v3 1/5] bswap.h: Add support for __BYTE_ORDER__

[Sebastian Andrzej Siewior <sebastian@breakpoint.cc>]

The __BYTE_ORDER__ define is provided by gcc (since ~v4.6), clang
(since ~v3.2) and icc (since ~16.0.3).

The __BYTE_ORDER and BYTE_ORDER macros are libc specific and are not
available on all supported platforms such as mingw.

Add support for the __BYTE_ORDER__ macro as a fallback.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
---
 compat/bswap.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/compat/bswap.h b/compat/bswap.h
index b34054f2bd728..0a457542dd76a 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -116,6 +116,12 @@ static inline uint64_t git_bswap64(uint64_t x)
 # define GIT_LITTLE_ENDIAN LITTLE_ENDIAN
 # define GIT_BIG_ENDIAN BIG_ENDIAN
 
+#elif defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && defined(__ORDER_BIG_ENDIAN__)
+
+# define GIT_BYTE_ORDER __BYTE_ORDER__
+# define GIT_LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
+# define GIT_BIG_ENDIAN __ORDER_BIG_ENDIAN__
+
 #else
 
 # define GIT_BIG_ENDIAN 4321
-- 
2.50.0