efi: drop glibc header and use pre-defined macros

This reverts 72dc626b3d and replace glibc
specific macros with compiler's pre-defined macros.

src/boot/efi/sha256.c

@@ -25,7 +25,7 @@
 
 #include "sha256.h"
 
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 # define SWAP(n)                                                        \
         (((n) << 24) | (((n) & 0xff00) << 8) | (((n) >> 8) & 0xff00) | ((n) >> 24))
 # define SWAP64(n)                              \

src/boot/efi/sha256.h

@@ -1,8 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
-#include <endian.h>
-
 #include <efi.h>
 #include <efilib.h>