Intel clamp modes:
- define BRW_TEXCOORDMODE_WRAP 0
- define BRW_TEXCOORDMODE_MIRROR 1
- define BRW_TEXCOORDMODE_CLAMP 2
- define BRW_TEXCOORDMODE_CUBE 3
- define BRW_TEXCOORDMODE_CLAMP_BORDER 4
- define BRW_TEXCOORDMODE_MIRROR_ONCE 5
GL_CLAMP is not natively supported.