Expose int64 compat profile
This exposes ARB_gpu_shader_int64 in compat profile. This is done for the purpose that our soft fp64 implementation relies on ARB_gpu_shader_int64 and we want ARB_gpu_shader_fp64 to work on compat profile. So, this can be done instead of !2438 (closed).
This fixes compilation errors with following tests on platforms with soft fp64:
- arb_separate_shader_object-ProgramUniform-coverage
- arb_gpu_shader_fp64-dlist-uniforms