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>

meson_options.txt

@@ -18,6 +18,10 @@ option('docbook_validation',
   type: 'boolean',
   value: false,
   description: 'Validate the intermediate DocBook XML during the documentation build')
+option('xml_catalog',
+  description: 'Path to XML catalog file',
+  type: 'string',
+  value: '')
 option('dtd_validation',
   description: 'Validate the protocol DTD (requires libxml2)',
   type: 'boolean',