build: Fix build and tests on macOS

This commit addresses several compatibility issues that prevented Wayland
from building and passing its test suite on macOS

Core and Compatibility changes:
- Emulate Linux behavior by explicitly setting O_NONBLOCK on connections
  (fixes blocking sendmsg issues on macOS).
- Fix compilation on platforms missing SOCK_CLOEXEC and MSG_CMSG_CLOEXEC.
- Implement wl_os_socket_peercred() using LOCAL_PEERPID for macOS.
- Ensure availability of struct itimerspec (required for POSIX Timers API).

Test suite fixes:
- Add socketpair_cloexec() wrapper to handle platforms without atomic
  SOCK_CLOEXEC support.
- Add implementation of memrchr() for platforms that do not provide it.
- Implement is_debugger_attached() for macOS to handle test timeouts.
- Fix tests to handle Mach-O binary format (instead of ELF).
- Update egl-symbols-check to support macOS *.dylib Mach-O libraries.

Build system:
- Add meson option 'xml_catalog' to allow specifying custom catalog paths.

Signed-off-by: Martin Lopatář <lopin@dataplex.cz>

tests/queue-test.c

@@ -44,6 +44,17 @@
 
 #define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])
 
+#ifdef __APPLE__
+static void *memrchr(const void *s, int c, size_t n) {
+	const unsigned char *p = (const unsigned char *)s;
+	while (n--) {
+		if (p[n] == (unsigned char)c)
+			return (void *)(p + n);
+	}
+	return NULL;
+}
+#endif
+
 static void
 registry_handle_global(void *data, struct wl_registry *registry,
 		       uint32_t id, const char *interface, uint32_t version)