[llvm-cov] Fix showing title when filtering and not outputting to a directory

[seaneveson]

Summary

Fix an accidental side effect of r314310 (https://reviews.llvm.org/D38280) where the coverage title was being written to stdout when filtering without an output directory.

[vsk]

It seems easy enough to add a regression test for this, and I think we should.

[seaneveson]

Extend a test that already checked for this to cover filtered output as well.

[vsk]

Great, thank you! Lgtm.

tools/llvm-cov/CodeCoverage.cpp

for (const auto &FileFunc : FilenameFunctionMap) {
 
       auto OSOrErr = Printer->createViewFile(File, /*InToplevel=*/false);
       if (Error E = OSOrErr.takeError()) {
         error("Could not create view file!", toString(std::move(E)));
         return 1;
       }
       auto OS = std::move(OSOrErr.get());
 
-      bool ShowTitle = true;
+      bool ShowTitle = ViewOpts.hasOutputDirectory();
       for (const auto *Function : Functions) {
         auto FunctionView = createFunctionView(*Function, *Coverage);
         if (!FunctionView) {
           warning("Could not read coverage for '" + Function->Name + "'.");
           continue;
         }
         FunctionView->print(*OS.get(), /*WholeFile=*/false,
                             /*ShowSourceName=*/true, ShowTitle);