Enable clang coverage

This is to align with build/soong to support clang coverage.
- support env CLANG_COVERAGE and CLANG_COVERAGE_CONTINUOUS_MODE.
- support kill -37 signal to dump coverage.
- support build clang coverage together with hwasan.

Bug: 309894892
Change-Id: I14f75d7fdfdf872d2db3bbceb2c10d6572bcfebf