Lacking GL_BLEND_COLOR
The macro GL_BLEND_COLOR is said [here](https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glBlendColor.xhtml) to be available on OpenGL 2.0 to OpenGL 4.5.

On my system `gl.h` it's available, but it's not generated on `glad.h`.

The file was generated with this command:
`--profile="core" --api="gl=3.3" --generator="c" --spec="gl" --extensions=""`