Mmap interceptor new option, Write Exec runtime detector

Summary: Following-up the refactoring of mmap interceptors, adding a new common option to detect PROT_WRITE|PROT_EXEC pages request.

Patch by David CARLIER

Reviewers: vitalybuka, vsk

Reviewed By: vitalybuka

Subscribers: krytarowski, #sanitizers

Differential Revision: https://reviews.llvm.org/D44194

llvm-svn: 327747