ARM stores the Thumb state in the least significant bit of the
function pointers. When compiling for ARM or Thumb, as all
instructions are at least 16-bit aligned, ignore the LSB when
computing the prefix hash location, so we can support both
pure Thumb and mixed ARM/Thumb binaries.
Fixes#62936
Reviewed By: MaskRay, simon_tatham
Differential Revision: https://reviews.llvm.org/D152484