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>

src/connection.c

@@ -316,6 +316,19 @@ wl_connection_set_max_buffer_size(struct wl_connection *connection,
 	ring_buffer_ensure_space(&connection->out, 0);
 }
 
+#ifdef __APPLE__
+static int fd_setfl_nonblock(int fd)
+{
+	int flags;
+
+	flags = fcntl(fd, F_GETFL, 0);
+	if (flags < 0)
+		return flags;
+
+	return fcntl(fd, F_SETFL, flags | O_NONBLOCK);
+}
+#endif
+
 struct wl_connection *
 wl_connection_create(int fd, size_t max_buffer_size)
 {
@@ -329,6 +342,10 @@ wl_connection_create(int fd, size_t max_buffer_size)
 
 	connection->fd = fd;
 
+#ifdef __APPLE__
+	fd_setfl_nonblock(fd);
+#endif
+
 	return connection;
 }