Throw an exception anytime we try to compile DrawIndex to MSL.
Throw an exception anytime we try to compile DrawIndex to MSL.

KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross