paxelf: use correct format string

On 32-bit platforms, mmap() larger than 2GB may fail.

This patch ensures that the correct size is printed and provides
parity with commit 90a0c6a.

Signed-off-by: Zach van Rijn <me@zv.io>
Closes: #18
Signed-off-by: Sam James <sam@gentoo.org>

paxelf.c

@@ -684,7 +684,7 @@ elfobj *_readelf_fd(const char *filename, int fd, size_t len, int read_only)
 
 	buffer = mmap(0, len, PROT_READ | (read_only ? 0 : PROT_WRITE), (read_only ? MAP_PRIVATE : MAP_SHARED), fd, 0);
 	if (buffer == MAP_FAILED) {
-		warn("mmap on '%s' of %li bytes failed :(", filename, (unsigned long)len);
+		warn("mmap on '%s' of %zu bytes failed :(", filename, len);
 		return NULL;
 	}