X86: Don't fold TEST into ADD ...@GOTTPOFF/GOTNTPOFF/INDNTPOFF

The linker may convert such an ADD into a LEA, so we must not
use the EFLAGS output.

This causes miscompiles with -fsanitize=null after
bacdf80f added
llvm.threadlocal.address -- previously, global variables were known to
be non-null, but the intrinsic is not currently known to return
nonnull. (That should be corrected, but it shouldn't've caused
miscompiles!)

Differential Revision: https://reviews.llvm.org/D131716