compat/bswap.h: don't assume MSVC is little-endian

In 1af265f (compat/bswap.h: simplify MSVC endianness
detection, 2020-11-08) we attempted to simplify code by assuming MSVC
builds will be for little-endian machines, since only unusably old
versions of MSVC supported big-endian MIPS and m68k architectures.

However, it's possible that MSVC could be ported to build for a
big-endian architecture again, so the simplification wasn't as
future-proof as hoped.

So let's go back to the old way of detecting MSVC, and then checking
architecture from a list of little-endian architecture macros.

Note that MSVC does not treat ARM64 as bi-endian, so we can safely treat
it as little-endian.

Helped-by: brian m. carlson <[email protected]>
Helped-by: Jeff King <[email protected]>
Helped-by: Johannes Schindelin <[email protected]>
Helped-by: Junio C Hamano <[email protected]>
Signed-off-by: Daniel Gurney <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dgurney

compat/bswap.h

@@ -74,7 +74,7 @@ static inline uint64_t git_bswap64(uint64_t x)
 }
 #endif
 
-#elif defined(_MSC_VER)
+#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM64))
 
 #include <stdlib.h>