Silence an illegal conversion warning in MSVC; NFC

The code previously required two levels of conversion, one from
SmallString to StringRef and one from StringRef to Regex. This made the
implicit conversion to StringRef be explicit instead.

clang-tools-extra/clang-tidy/GlobList.cpp

@@ -39,7 +39,7 @@ static llvm::Regex consumeGlob(StringRef &GlobList) {
     RegexText.push_back(C);
   }
   RegexText.push_back('$');
-  return {RegexText};
+  return {RegexText.str()};
 }
 
 GlobList::GlobList(StringRef Globs, bool KeepNegativeGlobs /* =true */) {