…atible with the standalone MinGW for Windows

When set to >= 0, the value of this cvar (in milliseconds) will be used for time-based shader effects.

`u_Color` was a vec4 that was being set from a `Color` object, which only has 8-bit precision per colour, so using up 4 times more memory than that to transfer it was quite atrocious. Instead, pack it into a uint32_t, then use `unpackUnorm4x8()` to unpack in the shader.

Also adds a macro for unpacking for hardware that doesn't support `GL_ARB_gpu_shader5`.

Add `u_ColorModulateColorGen` for use with shaders other than `cameraEffects`, since the latter can get an arbitrary vec4 for it. All other shaders only use 12 distinct states of `u_ColorModulateColorGen`, encoded as 5 bits. Also adds `u_ColorModulateLightFactor` as a global uniform, to be able to put the `genericMaterial` shader struct into 8 bytes.

Fixes an issue with material shader post-processing that was removing global uniforms that had similar names to a non-global one.

Move the multiplication by tr.mapLightFactor to the generic shader, store it in `u_ColorModulateColorGen`.

`tr.mapLightFactor` is already in `u_ColorModulateColorGen` anyway, so there's no need for the extra uniform.

Also fixes extra bits beng added to the `lightFactor` part `SetUniform_ColorModulateColorGen` in some cases.