bswap.h: define GIT_LITTLE_ENDIAN on msvc as little endian

The Microsoft Visual C++ (MSVC) compiler (as of Visual Studio 2022
version 17.13.6) does not define __BYTE_ORDER__ and its C-library does
not define __BYTE_ORDER. The compiler is supported only on arm64 and x86
which are all little endian.

Define GIT_BYTE_ORDER on msvc as little endian to avoid further checks.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sebastianas

compat/bswap.h

@@ -81,6 +81,10 @@ static inline uint64_t git_bswap64(uint64_t x)
 #define bswap32(x) _byteswap_ulong(x)
 #define bswap64(x) _byteswap_uint64(x)
 
+#define GIT_LITTLE_ENDIAN 1234
+#define GIT_BIG_ENDIAN 4321
+#define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN
+
 #endif
 
 #if defined(bswap32)
@@ -122,7 +126,7 @@ static inline uint64_t git_bswap64(uint64_t x)
 # define GIT_LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
 # define GIT_BIG_ENDIAN __ORDER_BIG_ENDIAN__
 
-#else
+#elif !defined(GIT_BYTE_ORDER)
 
 # define GIT_BIG_ENDIAN 4321
 # define GIT_LITTLE_ENDIAN 1234