The build bots caught two additional pre-existing problems exposed by the test change part of my change https://reviews.llvm.org/D91339, when expensive checks are enabled. This fixes one of them.
X86 has CALL64r and CALL32r opcodes, where CALL64r takes a 64-bit register, and CALL32r takes a 32-bit register. CALL64r can only be used in 64-bit mode, CALL32r can only be used in 32-bit mode. LLVM would assume that after picking the appropriate CALLr opcode, a pointer-sized register would be a valid operand, but in x32 mode, a 64-bit mode, pointers are 32 bits. In this mode, it is invalid to directly pass a pointer to CALL64r, it needs to be extended to 64 bits first.