[sanitizer-coverage] emit __sanitizer_cov_trace_pc_guard w/o a preceding 'if' by default. Update the docs, also add deprecation notes around other parts of sanitizer coverage

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292862 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed