kernel32/tests: Add sxs tests.

dlls/kernel32/tests/dummy.c

-/* nothing here */
+#include <windows.h>
+
+static HINSTANCE instance;
+
+BOOL WINAPI DllMain(HINSTANCE instance_new, DWORD reason, LPVOID reserved)
+{
+     switch (reason)
+    {
+        case DLL_PROCESS_ATTACH:
+            instance = instance_new;
+            break;
+    }
+
+    return TRUE;
+}
+
+WINAPI void get_path(char *buffer, int buffer_size)
+{
+    GetModuleFileNameA(instance, buffer, buffer_size);
+}

dlls/kernel32/tests/dummy.spec

-# nothing here
+@ stdcall get_path(ptr long)