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.c

@@ -50,7 +50,7 @@ int _tmain(int argc, TCHAR* argv[]) {
         }
     }
 
-    int max_arg = argc + 20;
+    int max_arg = argc + 22;
     const TCHAR **exec_argv = malloc((max_arg + 1) * sizeof(*exec_argv));
     int arg = 0;
     if (getenv("CCACHE"))
@@ -84,11 +84,6 @@ int _tmain(int argc, TCHAR* argv[]) {
         exec_argv[arg++] = _T("-DWINAPI_FAMILY=WINAPI_FAMILY_APP");
         // the Windows Store API only supports Windows Unicode (some rare ANSI ones are available)
         exec_argv[arg++] = _T("-DUNICODE");
-        // add the minimum runtime to use for UWP targets
-        exec_argv[arg++] = _T("-Wl,-lwindowsapp");
-        // This still requires that the toolchain (in particular, libc++.a) has
-        // been built targeting UCRT originally.
-        exec_argv[arg++] = _T("-Wl,-lucrtapp");
         // force the user of Universal C Runtime
         exec_argv[arg++] = _T("-D_UCRT");
     }
@@ -104,6 +99,19 @@ int _tmain(int argc, TCHAR* argv[]) {
     for (int i = 1; i < argc; i++)
         exec_argv[arg++] = argv[i];
 
+    if (target_os && !_tcscmp(target_os, _T("mingw32uwp"))) {
+        // Default linker flags; passed after any user specified -l options,
+        // to let the user specified libraries take precedence over these.
+
+        exec_argv[arg++] = _T("--start-no-unused-arguments");
+        // add the minimum runtime to use for UWP targets
+        exec_argv[arg++] = _T("-Wl,-lwindowsapp");
+        // This still requires that the toolchain (in particular, libc++.a) has
+        // been built targeting UCRT originally.
+        exec_argv[arg++] = _T("-Wl,-lucrtapp");
+        exec_argv[arg++] = _T("--end-no-unused-arguments");
+    }
+
     exec_argv[arg] = NULL;
     if (arg >= max_arg) {
         fprintf(stderr, "Too many options added\n");

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