Detect the endianness with CMake (!111)

## What is the bug

The endianness detection in `src/util_hash.c` produces a false result on macOS with GCC 13 or later. For whatever reason, [`#include <sys/param.h>`](https://gitlab.dkrz.de/icon-libraries/libfortran-support/-/blob/316d3dc6edb6ef0f4f1b9adaf9f3cb27a7bb831a/src/util_hash.c#L49) does not define the `__DARWIN_BYTE_ORDER` and `__DARWIN_LITTLE_ENDIAN` macros when [`#define _POSIX_C_SOURCE 200112L`](https://gitlab.dkrz.de/icon-libraries/libfortran-support/-/blob/316d3dc6edb6ef0f4f1b9adaf9f3cb27a7bb831a/src/util_hash.c#L45). And that leads to the wrong values of the `HASH_LITTLE_ENDIAN` and `HASH_BIG_ENDIAN` macros. See also https://gitlab.dkrz.de/icon/icon-mpim/-/merge_requests/684#note_300951

.

## How do you fix it

The endianness detection is delegated to CMake.

Approved-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Merged-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Changelog: bugfix

src/CMakeLists.txt

@@ -15,6 +15,9 @@ check_include_files("link.h" HAVE_LINK_H)
 check_include_files("unwind.h" HAVE_UNWIND_H)
 check_include_files("sys/resource.h" HAVE_GETRUSAGE)
 
+include(TestBigEndian)
+test_big_endian(HAVE_BIG_ENDIAN)
+
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in
                ${CMAKE_CURRENT_BINARY_DIR}/config.h)
 

src/config.h.in

@@ -16,3 +16,5 @@
 #cmakedefine HAVE_UNWIND_H @HAVE_UNWIND_H@
 
 #cmakedefine HAVE_GETRUSAGE @HAVE_GETRUSAGE@
+
+#cmakedefine HAVE_BIG_ENDIAN @HAVE_BIG_ENDIAN@

src/util_hash.c

@@ -42,63 +42,21 @@
  * -------------------------------------------------------------------------------
  */
 
-#define _POSIX_C_SOURCE 200112L
+#include "config.h"
 
-#include <stdint.h> /* defines uint32_t etc */
-
-#include <sys/param.h> /* attempt to define endianness */
-
-#if (defined(__APPLE__) && defined(__MACH__))
-
-#if (defined(__DARWIN_BYTE_ORDER) \
-     && (__DARWIN_BYTE_ORDER == __DARWIN_LITTLE_ENDIAN))
-#define HASH_LITTLE_ENDIAN 1
-#define HASH_BIG_ENDIAN 0
-#else
-#define HASH_LITTLE_ENDIAN 0
-#define HASH_BIG_ENDIAN 1
-#endif
+#include "util_hash.h"
 
-#elif defined(_AIX)
+#include <stddef.h>
+#include <stdint.h>
 
-#if (defined(BYTE_ORDER) && (BYTE_ORDER == LITTLE_ENDIAN))
-#define HASH_LITTLE_ENDIAN 1
-#define HASH_BIG_ENDIAN 0
-#else
+#ifdef HAVE_BIG_ENDIAN
 #define HASH_LITTLE_ENDIAN 0
 #define HASH_BIG_ENDIAN 1
-#endif
-
-#elif defined(__linux)
-
-#include <endian.h>
-
-#if (defined(__BYTE_ORDER) && (__BYTE_ORDER == __LITTLE_ENDIAN))
-#define HASH_LITTLE_ENDIAN 1
-#define HASH_BIG_ENDIAN 0
 #else
-#define HASH_LITTLE_ENDIAN 0
-#define HASH_BIG_ENDIAN 1
-#endif
-
-#elif defined(_SX)
-
-#define HASH_LITTLE_ENDIAN 0
-#define HASH_BIG_ENDIAN 1
-
-#elif defined(__NEC__)
-
 #define HASH_LITTLE_ENDIAN 1
 #define HASH_BIG_ENDIAN 0
-
-#else
-
-#error "Couldn't determine endianness."
-
 #endif
 
-#include "util_hash.h"
-
 #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
 
 /*

src/util_hash.h

@@ -12,6 +12,7 @@
 #ifndef UTIL_HASH_H
 #define UTIL_HASH_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 #ifdef __cplusplus