[xray] Avoid text relocations in trampolines for ARM/AArch64

Summary: Switch to pc-relative lookup of the xray handler function to avoid text relocations.

Reviewers: MaskRay, dberris, johnislarry

Subscribers: kristof.beyls, danielkiss, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D78595