Allowlist for SanitizerCoverage

[LeoneChen]

clang provide option fsanitize-coverage-allowlist to pass allow list to SanitizerCoverage, it passes option in code like below

static void addSanitizers(const Triple &TargetTriple,
                          const CodeGenOptions &CodeGenOpts,
                          const LangOptions &LangOpts, PassBuilder &PB) {
    MPM.addPass(SanitizerCoveragePass(
        SancovOpts, CodeGenOpts.SanitizeCoverageAllowlistFiles,
        CodeGenOpts.SanitizeCoverageIgnorelistFiles));
    ...
}

However, rust seems only can use -Cllvm-args to pass option registered by cl::opt etc., thus has no chance to pass allowlist