Instrument: Fix load type of pre-existing builtin (#2575)
Instrument: Fix load type of pre-existing builtin (#2575)

Builtins may be declared int, so load with its pointee type and cast
to uint if needed.
dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,antiagainst/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,antiagainst/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,KhronosGroup/SPIRV-Tools,antiagainst/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,KhronosGroup/SPIRV-Tools