egl: MacOS platform guard around pthread_condattr_setclock()

This patch disabled the call to pthread_condattr_setclock on MacOS/Apple platforms.
This funciton is missing from the the Xcode pthread implemetation.

Acked-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28130>

src/egl/drivers/dri2/egl_dri2.c

@@ -3335,6 +3335,7 @@ dri2_create_sync(_EGLDisplay *disp, EGLenum type, const EGLAttrib *attrib_list)
          goto fail;
       }
 
+#if !defined(__APPLE__) && !defined(__MACOSX)
       /* change clock attribute to CLOCK_MONOTONIC */
       ret = pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
 
@@ -3342,6 +3343,7 @@ dri2_create_sync(_EGLDisplay *disp, EGLenum type, const EGLAttrib *attrib_list)
          _eglError(EGL_BAD_ACCESS, "eglCreateSyncKHR");
          goto fail;
       }
+#endif
 
       ret = pthread_cond_init(&dri2_sync->cond, &attr);