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/clang-target-wrapper.sh

@@ -74,8 +74,9 @@ mingw32uwp)
     FLAGS="$FLAGS -DUNICODE"
     # add the minimum runtime to use for UWP targets
     FLAGS="$FLAGS -Wl,-lwindowsapp"
-    # This requires that the default crt is ucrt.
-    FLAGS="$FLAGS -Wl,-lvcruntime140_app"
+    # This still requires that the toolchain (in particular, libc++.a) has
+    # been built targeting UCRT originally.
+    FLAGS="$FLAGS -Wl,-lucrtapp"
     # Force the Universal C Runtime
     FLAGS="$FLAGS -D_UCRT"
     ;;