[Driver] Make -fsanitize=kcfi,function incompatible

A -fsanitize=kcfi instrumented function has a special instruction/data
before the function entry at a fixed offset.
A -fsanitize=function instrumented function has special instruction/data
after the function entry at a fixed offset (may change to *before* in D148665).

The two instrumentations are not intended to be used together and will become
incompatible after D148665.

Reviewed By: samitolvanen

Differential Revision: https://reviews.llvm.org/D148671