libbpf: Fix endianness macro usage for some compilers

Using endian.h and its endianness macros makes this code build in a
wider range of compilers, as some don't have those macros
(__BYTE_ORDER__, __ORDER_LITTLE_ENDIAN__, __ORDER_BIG_ENDIAN__),
so use instead endian.h's macros (__BYTE_ORDER, __LITTLE_ENDIAN,
__BIG_ENDIAN) which makes this code even shorter :-)
Acked-by: Andrii Nakryiko <andriin@fb.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: 12ef5634 ("libbpf: simplify endianness check")
Fixes: e6c64855 ("libbpf: add btf__parse_elf API to load .BTF and .BTF.ext")
Link: https://lkml.kernel.org/n/tip-eep5n8vgwcdphw3uc058k03u@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/btf.c

 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /* Copyright (c) 2018 Facebook */
 
+#include <endian.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -419,9 +420,9 @@ struct btf *btf__new(__u8 *data, __u32 size)
 
 static bool btf_check_endianness(const GElf_Ehdr *ehdr)
 {
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#if __BYTE_ORDER == __LITTLE_ENDIAN
 	return ehdr->e_ident[EI_DATA] == ELFDATA2LSB;
-#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#elif __BYTE_ORDER == __BIG_ENDIAN
 	return ehdr->e_ident[EI_DATA] == ELFDATA2MSB;
 #else
 # error "Unrecognized __BYTE_ORDER__"

tools/lib/bpf/libbpf.c

@@ -20,6 +20,7 @@
 #include <inttypes.h>
 #include <string.h>
 #include <unistd.h>
+#include <endian.h>
 #include <fcntl.h>
 #include <errno.h>
 #include <asm/unistd.h>
@@ -612,10 +613,10 @@ static int bpf_object__elf_init(struct bpf_object *obj)
 
 static int bpf_object__check_endianness(struct bpf_object *obj)
 {
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#if __BYTE_ORDER == __LITTLE_ENDIAN
 	if (obj->efile.ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
 		return 0;
-#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#elif __BYTE_ORDER == __BIG_ENDIAN
 	if (obj->efile.ehdr.e_ident[EI_DATA] == ELFDATA2MSB)
 		return 0;
 #else