wrappers: For UWP, pass the default -lwindowsapp after user specified options

This matches how the compiler driver normally includes default
linked libraries; the user provided -l flags are passed first,
followed by the compiler's default ones. That allows a user
specified library to override the default ones.

This makes sure that if a user provides -lwindowsappcompat, it
gets linked before -lwindowsapp, which makes a difference for
symbols that are provided in both (such as e.g. LoadLibraryW).

wrappers/clang-target-wrapper.sh

@@ -71,6 +71,7 @@ aarch64)
     # SEH is the default for aarch64.
     ;;
 esac
+LINKER_FLAGS=""
 case $TARGET_OS in
 mingw32uwp)
     # the UWP target is for Windows 10
@@ -79,11 +80,18 @@ mingw32uwp)
     FLAGS="$FLAGS -DWINAPI_FAMILY=WINAPI_FAMILY_APP"
     # the Windows Store API only supports Windows Unicode (some rare ANSI ones are available)
     FLAGS="$FLAGS -DUNICODE"
+
+    # Default linker flags; passed after any user specified -l options,
+    # to let the user specified libraries take precedence over these.
+
     # add the minimum runtime to use for UWP targets
-    FLAGS="$FLAGS -Wl,-lwindowsapp"
+    LINKER_FLAGS="$LINKER_FLAGS --start-no-unused-arguments"
+    LINKER_FLAGS="$LINKER_FLAGS -Wl,-lwindowsapp"
     # This still requires that the toolchain (in particular, libc++.a) has
     # been built targeting UCRT originally.
-    FLAGS="$FLAGS -Wl,-lucrtapp"
+    LINKER_FLAGS="$LINKER_FLAGS -Wl,-lucrtapp"
+    LINKER_FLAGS="$LINKER_FLAGS --end-no-unused-arguments"
+
     # Force the Universal C Runtime
     FLAGS="$FLAGS -D_UCRT"
     ;;
@@ -96,4 +104,4 @@ FLAGS="$FLAGS -stdlib=libc++"
 FLAGS="$FLAGS -fuse-ld=lld"
 FLAGS="$FLAGS --end-no-unused-arguments"
 
-$CCACHE "$CLANG" $FLAGS "$@"
+$CCACHE "$CLANG" $FLAGS "$@" $LINKER_FLAGS