[WebAssembly] Add an "explicit" keyword to a constructor.

llvm-svn: 290345
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
index f718324..d0e0eec 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
@@ -46,7 +46,7 @@
                          const MCSubtargetInfo &STI) const override;
 
 public:
-  WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii) : MCII(mcii) {}
+  explicit WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii) : MCII(mcii) {}
 };
 } // end anonymous namespace