[sanitizer] Decorate /proc/self/maps better.

Summary:
Refactor the way /proc/self/maps entries are annotated to support most
(all?) posix platforms, with a special implementation for Android.
Extend the set of decorated Mmap* calls.

Replace shm_open with internal_open("/dev/shm/%s"). Shm_open is
problematic because it calls libc open() which may be intercepted.

Generic implementation has limits (max number of files under /dev/shm is
64K on my machine), which can be conceivably reached when sanitizing
multiple programs at once. Android implemenation is essentially free, and
enabled by default.

The test in sanitizer_common is copied to hwasan and not reused directly
because hwasan fails way too many common tests at the moment.

Reviewers: pcc, vitalybuka

Subscribers: srhines, kubamracek, jfb, llvm-commits, kcc

Differential Revision: https://reviews.llvm.org/D57720

llvm-svn: 353255