mac: Fix build with 10.9 SDK

Without this, the compiler complains about `GL_TEXTURE_RECTANGLE_ARB` etc not being declared.

(similar to fix in upstream commit [f52fe5854ece2fe8ff5093060e2274972311d083](https://chromium.googlesource.com/chromium/src/+/f52fe5854ece2fe8ff5093060e2274972311d083))