More explicit message when failing to find a mandatory cfi ressource file

[serge-sans-paille]

Summary

Compiler-rt doesn't provide support file for cfi on s390x ad ppc64le (at least). When trying to use the flag, we get a file error.
This is an attempt at making the error more explicit, maybe we should also suggest passing -fno-sanitize-ignorelist?

[thakis]

Test?

[serge-sans-paille]

Updating test case / sorry for the delay

[MaskRay]

clang/include/clang/Basic/DiagnosticDriverKinds.td

209

missing sanitizer ignorelist:

clang/include/clang/Basic/DiagnosticDriverKinds.td

def warn_drv_missing_plugin_name : Warning<
   InGroup<InvalidCommandLineArgument>;
 def warn_drv_missing_plugin_arg : Warning<
   "missing plugin argument for plugin %0 in %1">,
   InGroup<InvalidCommandLineArgument>;
 def err_drv_invalid_libcxx_deployment : Error<
   "invalid deployment target for -stdlib=libc++ (requires %0 or later)">;
 def err_drv_invalid_argument_to_option : Error<
   "invalid argument '%0' to -%1">;
+def err_drv_missing_sanitizer_ignorelist : Error<
+  "missing required sanitizer ignorelist: '%0'">;
 def err_drv_malformed_sanitizer_ignorelist : Error<
   "malformed sanitizer ignorelist: '%0'">;
 def err_drv_malformed_sanitizer_coverage_allowlist : Error<
   "malformed sanitizer coverage allowlist: '%0'">;
 def err_drv_malformed_sanitizer_coverage_ignorelist : Error<
   "malformed sanitizer coverage ignorelist: '%0'">;
 def err_drv_duplicate_config : Error<
   "no more than one option '--config' is allowed">;

clang/lib/Driver/SanitizerArgs.cpp

for (auto BL : Ignorelists) {
 
     clang::SmallString<64> Path(D.ResourceDir);
     llvm::sys::path::append(Path, "share", BL.File);
     if (D.getVFS().exists(Path))
       IgnorelistFiles.push_back(std::string(Path.str()));
     else if (BL.Mask == SanitizerKind::CFI && DiagnoseErrors)
       // If cfi_ignorelist.txt cannot be found in the resource dir, driver
       // should fail.
-      D.Diag(clang::diag::err_drv_no_such_file) << Path;
+      D.Diag(clang::diag::err_drv_missing_sanitizer_ignorelist) << Path;
   }
   validateSpecialCaseListFormat(
       D, IgnorelistFiles, clang::diag::err_drv_malformed_sanitizer_ignorelist,
       DiagnoseErrors);
 }
 
 /// Parse -f(no-)?sanitize-(coverage-)?(white|ignore)list argument's values,
 /// diagnosing any invalid file paths and validating special case list format.