Cleanup and generalize -shared-libasan.

Summary:
* Rename -shared-libasan to -shared-libsan, keeping the old name as alias.
* Add -static-libsan for targets that default to shared.
* Remove an Android special case. It is now possible (but untested) to use static compiler-rt libraries there.
* Support libclang_rt.ubsan_standalone as a shared library.

Unlike GCC, this change applies -shared-libsan / -static-libsan to all sanitizers.
I don't see a point in multiple flags like -shared-libubsan, considering that most sanitizers
are not compatible with each other, and each link has basically a single shared/static choice.

Reviewers: vitalybuka, kcc, rsmith

Subscribers: srhines, cfe-commits

Differential Revision: https://reviews.llvm.org/D38525

llvm-svn: 315015