Add explicit keywords.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48801 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/CommandLine.cpp b/lib/Support/CommandLine.cpp
index b3f32e8..24f220d 100644
--- a/lib/Support/CommandLine.cpp
+++ b/lib/Support/CommandLine.cpp
@@ -931,7 +931,7 @@
   }
 
 public:
-  HelpPrinter(bool showHidden) : ShowHidden(showHidden) {
+  explicit HelpPrinter(bool showHidden) : ShowHidden(showHidden) {
     EmptyArg = 0;
   }