wrappers: Use -lucrtapp instead of -lvcruntime140_app

Passing -lucrt* to the clang driver inhibits the implicit default
-lmsvcrt, so this ends up only using libucrtapp.a instead of libucrt.a.

This still requires that the default crt was ucrt, as the prebuilt
libc++.a needs to have been built for the right crt.

wrappers/ld-wrapper.sh

@@ -34,7 +34,7 @@ esac
 FLAGS="-m $M"
 case $TARGET_OS in
 mingw32uwp)
-    FLAGS="$FLAGS -lwindowsapp -lvcruntime140_app"
+    FLAGS="$FLAGS -lwindowsapp -lucrtapp"
     ;;
 esac
 ld.lld $FLAGS "$@"