[Support] Fix clang warning in widenPath NFC

[andrewng]

Summary

Fix warning when compiled with clang-cl.

[aganea]

Looks good, thanks!

llvm/lib/Support/Windows/Path.inc

std::error_code widenPath(const Twine &Path8, SmallVectorImpl<wchar_t> &Path16,
                           size_t MaxPathLen) {
   assert(MaxPathLen <= MAX_PATH);
 
   // Several operations would convert Path8 to SmallString; more efficient to do
   // it once up front.
   SmallString<MAX_PATH> Path8Str;
   Path8.toVector(Path8Str);
 
-  std::error_code EC = UTF8ToUTF16(Path8Str, Path16);
-  if (EC)
+  if (std::error_code EC = UTF8ToUTF16(Path8Str, Path16))
     return EC;
 
   const bool IsAbsolute = llvm::sys::path::is_absolute(Path8);
   size_t CurPathLen;
   if (IsAbsolute)
     CurPathLen = 0; // No contribution from current_path needed.
   else {
     CurPathLen = ::GetCurrentDirectoryW(
         0, NULL); // Returns the size including the null terminator.
     if (CurPathLen == 0)
       return mapWindowsError(::GetLastError());
   }
 
   const char *const LongPathPrefix = "\\\\?\\";
 
   if ((Path16.size() + CurPathLen) < MaxPathLen ||
       Path8Str.startswith(LongPathPrefix))
     return std::error_code();
 
   if (!IsAbsolute) {
-    if (EC = llvm::sys::fs::make_absolute(Path8Str))
+    if (std::error_code EC = llvm::sys::fs::make_absolute(Path8Str))
       return EC;
   }
 
   // Remove '.' and '..' because long paths treat these as real path components.
   llvm::sys::path::remove_dots(Path8Str, true);
 
   const StringRef RootName = llvm::sys::path::root_name(Path8Str);
   assert(!RootName.empty() &&