[clang][deps] Move injection of `-Wno-error` from `clang-scan-deps` to `DependencyScanning` library

[jansvoboda11]

Summary

This moves another piece of logic specific to clang-scan-deps into the DependencyScanning library. This makes it easier to check how the original command-line looked like in the library and will enable the library to stop inventing -Wno-error for modular dependencies (see D104036).

[arphaman]

Thanks, LGTM

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
     // Create a compiler instance to handle the actual work.
     CompilerInstance Compiler(std::move(PCHContainerOps));
     Compiler.setInvocation(std::move(Invocation));
 
     // Don't print 'X warnings and Y errors generated'.
     Compiler.getDiagnosticOpts().ShowCarets = false;
     // Don't write out diagnostic file.
     Compiler.getDiagnosticOpts().DiagnosticSerializationFile.clear();
+    // Don't treat warnings as errors.
+    Compiler.getDiagnosticOpts().Warnings.push_back("no-error");
     // Create the compiler's actual diagnostics engine.
     Compiler.createDiagnostics(DiagConsumer, /*ShouldOwnClient=*/false);
     if (!Compiler.hasDiagnostics())
       return false;
 
     // Use the dependency scanning optimized file system if we can.
     if (DepFS) {
       const CompilerInvocation &CI = Compiler.getInvocation();

clang/tools/clang-scan-deps/ClangScanDeps.cpp

AdjustingCompilations->appendArgumentsAdjuster(
         // The clang-cl driver passes "-o -" to the frontend. Inject the real
         // file here to ensure "-MT" can be deduced if need be.
         if (ClangCLMode && !LastO.empty()) {
           AdjustedArgs.push_back("/clang:-o");
           AdjustedArgs.push_back("/clang:" + LastO);
         }
         AdjustedArgs.push_back("-Xclang");
         AdjustedArgs.push_back("-sys-header-deps");
-        AdjustedArgs.push_back("-Wno-error");
 
         if (!HasResourceDir) {
           StringRef ResourceDir =
               ResourceDirCache.findResourceDir(Args, ClangCLMode);
           if (!ResourceDir.empty()) {
             AdjustedArgs.push_back("-resource-dir");
             AdjustedArgs.push_back(std::string(ResourceDir));
           }