Allow -fsanitize=function on all targets

Functions instrumented with -fsanitize=function have two words before
the function label: a signature and a RTTI proxy.
Instrumented call sites check the signature first to skip checks
for uninstrumented callees.

The code is generic and works for all targets supporting C++ RTTI.
Change clangDriver to allow all targets. Add tests for Armv8.5
Branch Target Identification and `-fpatchable-function-entry=`.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D148573