Basic: silence MSVC pedantic warning (NFC)

The constructor here required multiple user-defined conversions which is
not exactly pedantically correct.  Add an explicit indicator that the
constructor being invoked is the `StringRef` constructor to convert the
`SmallString` to a `StringRef` which can then be implicitly converted to
the `Optional<StringRef>`.  This silences a MSVC warning (clang should
catch this with `-pedantic`).

Author: compnerd

lib/Basic/Default/Task.inc

@@ -84,7 +84,10 @@ bool Task::execute() {
   }
 
   Optional<StringRef> Redirects[] = {
-      None, {StdoutPath}, {SeparateErrors ? StderrPath : StdoutPath}};
+      None,
+      StringRef{StdoutPath},
+      StringRef{SeparateErrors ? StderrPath : StdoutPath},
+  };
 
   bool ExecutionFailed = false;
   PI = llvm::sys::ExecuteNoWait(ExecPath, llvm::toStringRefArray(Argv.data()),