Add explicit keywords.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48801 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AsmParser/LLLexer.h b/lib/AsmParser/LLLexer.h
index 7eaa9f9..8b44b14 100644
--- a/lib/AsmParser/LLLexer.h
+++ b/lib/AsmParser/LLLexer.h
@@ -30,7 +30,7 @@
     
     std::string TheError;
   public:
-    LLLexer(MemoryBuffer *StartBuf);
+    explicit LLLexer(MemoryBuffer *StartBuf);
     ~LLLexer() {}
 
     const char *getTokStart() const { return TokStart; }