clang cannot compile these files at the default optimization level

Index: engine/Makefile.in
--- engine/Makefile.in.orig
+++ engine/Makefile.in
@@ -163,13 +163,13 @@ gforth-fi$(OPT)$(EC)$(EXE):	$(OBJECTS_FI) $(AOBJECTS) 
 	$(GCCLD) $(LDFLAGS) $(OBJECTS_FI) $(AOBJECTS) $(LDLIBS) -o $@
 
 engine.s:	$(ENGINE_FAST_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -S $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -S $(srcdir)/engine.c
 
 engine$(OPT).o:	$(ENGINE_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DGFORTH_DEBUGGING -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -DGFORTH_DEBUGGING -o $@ -c $(srcdir)/engine.c
 
 engine2$(OPT).o:	$(ENGINE_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DGFORTH_DEBUGGING -DENGINE=2 -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -DGFORTH_DEBUGGING -DENGINE=2 -o $@ -c $(srcdir)/engine.c
 
 engine-native$(OPT).o:$(ENGINE_FAST_DEPS)
 		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DNO_IP -o $@ -c $(srcdir)/engine.c
@@ -181,16 +181,16 @@ engine-native3$(OPT).o:$(ENGINE_FAST_DEPS)
 		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DNO_IP -DENGINE=3 -o $@ -c $(srcdir)/engine.c
 
 engine-fast$(OPT).o:	$(ENGINE_FAST_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -o $@ -c $(srcdir)/engine.c
 
 engine-fast2$(OPT).o:	$(ENGINE_FAST_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DENGINE=2 -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -DENGINE=2 -o $@ -c $(srcdir)/engine.c
 
 engine-itc$(OPT).o:	$(ENGINE_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DINDIRECT_THREADED -DGFORTH_DEBUGGING -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -DINDIRECT_THREADED -DGFORTH_DEBUGGING -o $@ -c $(srcdir)/engine.c
 
 engine-ditc$(OPT).o:	$(ENGINE_DEPS)
-		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DDOUBLY_INDIRECT -o $@ -c $(srcdir)/engine.c
+		$(GCC) $(CFLAGS2) $(CPPFLAGS) -O0 $(ENGINE_FLAGS) -DDOUBLY_INDIRECT -o $@ -c $(srcdir)/engine.c
 
 engine-prof$(OPT).o:	$(ENGINE_DEPS)
 		$(GCC) $(CFLAGS2) $(CPPFLAGS) $(ENGINE_FLAGS) -DVM_PROFILING -o $@ -c $(srcdir)/engine.c