'GL/gl.h', 'GL/glx.h' file not found Error on Mac OS Mojave

Mac OS (Mojave): 10.14.4 Meson: 0.49.2 Ninja: 1.9.0

The errors below occur.

../subprojects/gst-plugins-base/tests/examples/gl/sdl/sdlshare2.c:28:10: fatal error: 'GL/gl.h' file not found

../subprojects/gst-plugins-base/tests/examples/gl/sdl/sdlshare.c:33:10: fatal error: 'GL/glx.h' file not found

It seems to be similar with #11 (closed) but not enough the solution for that. How should I handle this type of errors?