Fix MinGW-related portability issues.

Create and use FMT* macros that are equivalent to the PRI* macros that
inttypes.h defines.  This allows uniform use of the Unix-specific format
specifiers, e.g. "%zu", as well as avoiding Windows-specific definitions
of e.g. PRIu64.

Add ffs()/ffsl() support for compiling with gcc.

Extract compatibility definitions of ENOENT, EINVAL, EAGAIN, EPERM,
ENOMEM, and ENORANGE into include/msvc_compat/windows_extra.h and
use the file for tests as well as for core jemalloc code.

test/unit/rtree.c

@@ -72,7 +72,7 @@ TEST_BEGIN(test_rtree_bits)
 				    &node, "rtree_get() should return "
 				    "previously set value and ignore "
 				    "insignificant key bits; i=%u, j=%u, k=%u, "
-				    "set key=%#"PRIxPTR", get key=%#"PRIxPTR, i,
+				    "set key=%#"FMTxPTR", get key=%#"FMTxPTR, i,
 				    j, k, keys[j], keys[k]);
 			}
 			assert_ptr_null(rtree_get(&rtree,