[compiler-rt] Add print_coverage_summary to silence SanitizerCoverage dump logs (#228039)

When running a test suite of SanitizerCoverage-instrumented binaries,
the `SanitizerCoverage: … PCs written` summary on stderr can poison
FileCheck and cause unexpected failures.

There is no way to turn that print off today. At most you can use
`log_path`, but that still creates a text file per process. We could
have guard it on the verbosity option, but that would change the default
and may regress consumers that rely on this output.

This PR adds `print_coverage_summary` (default true). Set
`print_coverage_summary=0` to keep the dump log disable; .sancov files
are still written. The same guard is used on the Fuchsia path.

The new lit test is a copy of sanitizer_coverage_trace_pc_guard.cpp,
adapted to check the default print and print_coverage_summary=0.

GitOrigin-RevId: e7f7422a14cfdd6d00fcf7e2e25bfd5a47897030