Apply clang-tidy's 'performance-faster-string-find' check to LLVM.

No functionality change intended.

llvm-svn: 288235
diff --git a/llvm/tools/llvm-cov/CodeCoverage.cpp b/llvm/tools/llvm-cov/CodeCoverage.cpp
index 153e5ed..0a9807a 100644
--- a/llvm/tools/llvm-cov/CodeCoverage.cpp
+++ b/llvm/tools/llvm-cov/CodeCoverage.cpp
@@ -742,7 +742,7 @@
 
   auto ModifiedTime = Status.getLastModificationTime();
   std::string ModifiedTimeStr = to_string(ModifiedTime);
-  size_t found = ModifiedTimeStr.rfind(":");
+  size_t found = ModifiedTimeStr.rfind(':');
   ViewOpts.CreatedTimeStr = (found != std::string::npos)
                                 ? "Created: " + ModifiedTimeStr.substr(0, found)
                                 : "Created: " + ModifiedTimeStr;