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>

doc/meson.build

@@ -22,8 +22,16 @@ if vers.version_compare('< 2.26.0')
 	error('Dot (Graphviz) 2.26 or later is required for building documentation, found @0@.'.format(vers))
 endif
 
+run_env = environment()
+if catalog_path != ''
+	if not catalog_path.startswith('/')
+		catalog_path = meson.project_source_root() / catalog_path
+	endif
+	run_env.set('XML_CATALOG_FILES', catalog_path)
+endif
+
 manpage_xsl = 'http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl'
-cmd = run_command(xsltproc, '--nonet', manpage_xsl, check: false)
+cmd = run_command(xsltproc, '--nonet', manpage_xsl, env: run_env, check: false)
 if cmd.returncode() != 0
 	error('The style sheet for man pages providing "@0@" was not found.'.format(manpage_xsl))
 endif