tests: add a test to make sure compiling forbidden UWP APIs fails

When building for UWP and works otherwise

run-tests.sh

@@ -38,6 +38,7 @@ TESTS_CPP_DLL="tlstest-lib"
 TESTS_SSP="stacksmash"
 TESTS_ASAN="stacksmash"
 TESTS_UBSAN="ubsan"
+TESTS_UWP="uwp-error"
 for arch in $ARCHS; do
     case $arch in
     i686|x86_64)
@@ -92,6 +93,29 @@ for arch in $ARCHS; do
         for test in $TESTS_SSP; do
             $arch-w64-$target_os-clang $test.c -o $TEST_DIR/$test.exe -fstack-protector-strong
         done
+        for test in $TESTS_UWP; do
+            set +e
+            # compilation should fail for UWP and WinRT
+            $arch-w64-$target_os-clang $test.c -o $TEST_DIR/$test.exe -Wimplicit-function-declaration -Werror
+            UWP_ERROR=$?
+            set -e
+            case $target_os in
+            mingw32uwp)
+                if [ $UWP_ERROR -eq 0 ]; then
+                    echo "UWP compilation should have failed for test $test!"
+                    exit 1
+                fi
+                ;;
+            *)
+                if [ $UWP_ERROR -eq 0 ]; then
+                    TESTS_EXTRA="$TESTS_EXTRA $test"
+                else
+                    echo "$test failed to compile for non-UWP target!"
+                    exit 1
+                fi
+                ;;
+            esac
+        done
         for test in $TESTS_ASAN; do
             case $arch in
             # Sanitizers on windows only support x86.

test/uwp-error.c

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2019 Steve Lhomme
+ *
+ * This file is part of llvm-mingw.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <windows.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+    UINT res = GetOEMCP();
+    fprintf(stderr, "Windows OEM CP is %u\n", res);
+    return 0;
+}