[asan] Add options -asan-detect-invalid-pointer-cmp and -asan-detect-invalid-pointer-sub options.

This is in preparation to a driver patch to add gcc 8's -fsanitize=pointer-compare and -fsanitize=pointer-subtract.
Disabled by default as this is still an experimental feature.

Reviewed By: morehouse, vitalybuka

Differential Revision: https://reviews.llvm.org/D59220

llvm-svn: 357157