fix some compilation issues

src/tests.c

@@ -36,6 +36,9 @@
 #include <kernel/terrain.h>
 #include <util/functions.h>
 #include <util/language.h>
+#include <util/log.h>
+
+#include <assert.h>
 
 int RunAllTests(void)
 {

src/tests.h

@@ -3,8 +3,6 @@ extern "C" {
 #endif
 
 #ifndef DISABLE_TESTS
-  struct building_type;
-  struct building;
   void test_cleanup(void);
 
   struct terrain_type * test_create_terrain(const char * name, unsigned int flags);