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/include/test/jemalloc_test.h.in

@@ -6,13 +6,16 @@
 #include <stdarg.h>
 #include <stdbool.h>
 #include <errno.h>
-#include <inttypes.h>
 #include <math.h>
 #include <string.h>
+#ifdef _WIN32
+#  include "msvc_compat/strings.h"
+#endif
 #include <sys/time.h>
 
 #ifdef _WIN32
 #  include <windows.h>
+#  include "msvc_compat/windows_extra.h"
 #else
 #  include <pthread.h>
 #endif