Removing LLVM_EXPLICIT, as MSVC 2012 was the last reason for requiring the macro. NFC; LLVM edition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229335 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Windows/WindowsSupport.h

@@ -92,7 +92,7 @@ public:
   }
 
   // True if Handle is valid.
-  LLVM_EXPLICIT operator bool() const {
+  explicit operator bool() const {
     return HandleTraits::IsValid(Handle) ? true : false;
   }