[TSan] Make sure we only collect non-TSan frames for memory operations...

[TSan] Make sure we only collect non-TSan frames for memory operations r=dvyukov,rsundahl,thetruestblue,wrotki,kubamracek!

A previous change [1] moved retrieval of the caller PC
(`__builtin_return_address(0)` via `CALLERPC`) from an
interface-boundary function into a shared helper function
`ExternalAccess`.  If this function does not get inlined, we fail to
collect the appropriate caller PC for the "TSan interface boundary".

[1] https://reviews.llvm.org/D32360

rdar://78489600

Differential Revision: https://reviews.llvm.org/D146264