Enable continuous coverage: use '%c' specifier in LLVM_PROFILE_FILE

Bug: http://b/194128476
Bug: http://b/210012154

- Do not use %c if coverage is enabled for bionic/libc.

Test: Run tests with this topic and verify coverage still works and also
test memory-mapped coverage (death tests, JNI code in CTS)

Change-Id: Id1ade9c6f45d69a1da912e3e57acd1d0197c11b5