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.

include/msvc_compat/windows_extra.h

@@ -0,0 +1,26 @@
+#ifndef MSVC_COMPAT_WINDOWS_EXTRA_H
+#define	MSVC_COMPAT_WINDOWS_EXTRA_H
+
+#ifndef ENOENT
+#  define ENOENT ERROR_PATH_NOT_FOUND
+#endif
+#ifndef EINVAL
+#  define EINVAL ERROR_BAD_ARGUMENTS
+#endif
+#ifndef EAGAIN
+#  define EAGAIN ERROR_OUTOFMEMORY
+#endif
+#ifndef EPERM
+#  define EPERM  ERROR_WRITE_FAULT
+#endif
+#ifndef EFAULT
+#  define EFAULT ERROR_INVALID_ADDRESS
+#endif
+#ifndef ENOMEM
+#  define ENOMEM ERROR_NOT_ENOUGH_MEMORY
+#endif
+#ifndef ERANGE
+#  define ERANGE ERROR_INVALID_DATA
+#endif
+
+#endif /* MSVC_COMPAT_WINDOWS_EXTRA_H */