darwin: Locate libffi with cc.find_library() rather than dependency()

Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>

meson.build

@@ -87,7 +87,12 @@ if get_option('libraries')
 		# Otherwise, assume that epoll(7) is supported natively.
 		epoll_dep = []
 	endif
-	ffi_dep = dependency('libffi')
+
+	if host_machine.system() == 'darwin'
+		ffi_dep = cc.find_library('ffi')
+	else
+		ffi_dep = dependency('libffi')
+	endif
 
 	decls = [
 		{ 'header': 'sys/signalfd.h', 'symbol': 'SFD_CLOEXEC' },

src/connection.c

@@ -40,7 +40,11 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <time.h>
+#ifdef __APPLE__
+#include <ffi/ffi.h>
+#else
 #include <ffi.h>
+#endif
 
 #include "wayland-util.h"
 #include "wayland-private.h"