Use Get/SetLastError on Win32

Using errno on win32 doesn't quite work, because the value set in a shared
library can't be read from e.g. an executable calling the function setting
errno.

At the same time, since buferror always uses errno/GetLastError, don't pass
it.

src/huge.c

@@ -168,7 +168,7 @@ huge_ralloc(void *ptr, size_t oldsize, size_t size, size_t extra,
 			 */
 			char buf[BUFERROR_BUF];
 
-			buferror(errno, buf, sizeof(buf));
+			buferror(buf, sizeof(buf));
 			malloc_printf("<jemalloc>: Error in mremap(): %s\n",
 			    buf);
 			if (opt_abort)