arb_texture_buffer_object/texture-buffer-size-clamp: handle large max tbo size

according to the ARB_texture_buffer_object spec, MAX_TEXTURE_BUFFER_SIZE_ARB can be returned as a double, enabling values larger than INT32_MAX

the test is not written to handle larger values, however, so a bit of surgery is required to enable this

core mesa does not allow allocations larger than UINT32_MAX, which requires further surgery to clamp there