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>

egl/wayland-egl-symbols-check

@@ -14,7 +14,10 @@ if ! test -n "$NM"; then
 	exit 99
 fi
 
-AVAIL_FUNCS="$($NM -D --format=bsd --defined-only $LIB | awk '{print $3}')"
+case "$LIB" in
+  *.dylib) AVAIL_FUNCS="$($NM -g --format=bsd --defined-only $LIB | awk '{sub(/^_/,"",$3);print $3}')" ;;
+  *.so|*.so.*) AVAIL_FUNCS="$($NM -D --format=bsd --defined-only $LIB | awk '{print $3}')" ;;
+esac
 
 # Official ABI, taken from the header.
 REQ_FUNCS="wl_egl_window_resize