[cxx-interop] Pass `--gcc-toolchain` to Clang driver when determining include paths
[cxx-interop] Pass `--gcc-toolchain` to Clang driver when determining include paths

glessard/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,apple/swift,benlangmuir/swift,JGiola/swift,apple/swift,glessard/swift,apple/swift,roambotics/swift,benlangmuir/swift,roambotics/swift,JGiola/swift,JGiola/swift,JGiola/swift,roambotics/swift,JGiola/swift,glessard/swift,benlangmuir/swift,roambotics/swift,apple/swift,benlangmuir/swift,glessard/swift,apple/swift,glessard/swift,benlangmuir/swift,roambotics/swift,glessard/swift,apple/swift