[llvm-cov] Use relative paths to file reports in -output-dir mode

This makes it possible to e.g copy a report to another filesystem.

llvm-svn: 274173
diff --git a/llvm/tools/llvm-cov/SourceCoverageView.cpp b/llvm/tools/llvm-cov/SourceCoverageView.cpp
index a4e9c43..08eb545 100644
--- a/llvm/tools/llvm-cov/SourceCoverageView.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageView.cpp
@@ -28,10 +28,14 @@
 }
 
 std::string CoveragePrinter::getOutputPath(StringRef Path, StringRef Extension,
-                                           bool InToplevel) {
+                                           bool InToplevel, bool Relative) {
   assert(Extension.size() && "The file extension may not be empty");
 
-  SmallString<256> FullPath(Opts.ShowOutputDirectory);
+  SmallString<256> FullPath;
+
+  if (!Relative)
+    FullPath.append(Opts.ShowOutputDirectory);
+
   if (!InToplevel)
     sys::path::append(FullPath, getCoverageDir());
 
@@ -51,7 +55,7 @@
   if (!Opts.hasOutputDirectory())
     return OwnedStream(&outs());
 
-  std::string FullPath = getOutputPath(Path, Extension, InToplevel);
+  std::string FullPath = getOutputPath(Path, Extension, InToplevel, false);
 
   auto ParentDir = sys::path::parent_path(FullPath);
   if (auto E = sys::fs::create_directories(ParentDir))