Helper static library for coverage/profile collection

Bug: http://b/128524141

This static library adds two different ways to trigger the Clang profile
runtime to flush GCOV profiles:
- a real-time signal (37) targeted to this process/pid
- a transistion of "coverage.flush" sysprop from "0" -> "1".

Test: libprofile-extras-test
Change-Id: I6bc8149b32ca1aebd4646b28150985b7b93ab33f
4 files changed