More explicit keywords.

llvm-svn: 40757
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 0fca985..055302f 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -46,7 +46,7 @@
 
   struct BranchFolder : public MachineFunctionPass {
     static char ID;
-    BranchFolder(bool defaultEnableTailMerge) : 
+    explicit BranchFolder(bool defaultEnableTailMerge) : 
         MachineFunctionPass((intptr_t)&ID) {
           switch (FlagEnableTailMerge) {
           case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;