Add workaround to translate casts from target ext types to int (#3689)
This patch should be reverted in the future as it supports translation
of invalid SPIR-V modules.
This is forward-porting from:
https://github.com/KhronosGroup/SPIRV-LLVM-Translator/pull/3476
This is workaround related to:
https://github.com/intel/llvm/commit/f34e5458aa63
Original commit:
https://github.com/KhronosGroup/SPIRV-LLVM-Translator/commit/daa7d18d7e42615