fix macOS compile issue for timespec_get (#183)

meson.build

@@ -282,6 +282,8 @@ config.set('TAISEI_BUILDCONF_LOG_FATAL_MSGBOX', (
     host_machine.system() == 'darwin' or
     not is_developer_build
 ))
+# fixes some build issues on macOS, see PR #183
+config.set('TAISEI_BUILDCONF_DARWIN_SOURCE', (host_machine.system() == 'darwin'))
 config.set('TAISEI_BUILDCONF_DEBUG_OPENGL', get_option('debug_opengl'))
 
 install_docs = get_option('docs') and host_machine.system() != 'emscripten'

src/util/compat.h

@@ -15,6 +15,13 @@
 #define _POSIX_C_SOURCE 200809L
 #endif
 
+// When compiling for Apple devices, the _POSIX_C_SOURCE option above messes with what header functions
+// are available to the compiler, and it'll complain that things like timespec_get, etc don't exist
+// even if Meson can detect them initially. Defining this fixes it.
+#ifdef TAISEI_BUILDCONF_DARWIN_SOURCE
+#define _DARWIN_C_SOURCE
+#endif
+
 // Common standard library headers
 #include <complex.h>
 #include <ctype.h>