run-tests: Wipe out an older libunwind.dll in the same way as libc++.dll

Ideally we'd wipe the whole test/<arch> directory before running
the tests (we do that if CLEAN is set), but here we only wipe out
the specific ones that can affect how new tests are built and linked.

run-tests.sh

@@ -104,8 +104,9 @@ for arch in $ARCHS; do
     TESTS_EXTRA=""
     [ -z "$CLEAN" ] || rm -rf $TEST_DIR
     # A leftover libc++.dll from a previous round will cause the linker to find it (and error out) instead of
-    # locating libc++.dll.a in a later include directory.
-    rm -f $TEST_DIR/libc++.dll
+    # locating libc++.dll.a in a later include directory. The same goes with
+    # libunwind.dll.
+    rm -f $TEST_DIR/libc++.dll $TEST_DIR/libunwind.dll
     mkdir -p $TEST_DIR
     for test in $TESTS_C; do
         $arch-w64-mingw32-clang $test.c -o $TEST_DIR/$test.exe