[llvm-cov] Fix a comment, NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294134 91177308-0d34-0410-b5e6-96231b3b80d8

Author: vedantk

Diff for: tools/llvm-cov/CodeCoverage.cpp

@@ -139,7 +139,7 @@ class CodeCoverageTool {
   /// A cache for demangled symbol names.
   StringMap<std::string> DemangledNames;
 
-  /// Errors and warnings which have not been printed.
+  /// A lock which guards printing to stderr.
   std::mutex ErrsLock;
 
   /// A container for input source file buffers.