redefining variables based on target

[Tanuz, Adam R]

Hello,
I am working on a project and am trying to move from the sun make
to the gnu make.  I have found that the following method for
switching between the debug option and the optimization option
doesn't work in gnu make.  Is their a way to do this in gnu?
I would appreciate any help at all.
 
CC68KOPTS = -Wall -fno-builtin $(CC_DEFINES) $(TST_FLG)

CC_68K = cc68k

#
all:= CC_68K += $(CC68KOPTS) -O2
all: $(EXEC) $(TEXEC)

debug := CC_68K += $(CC68KOPTS) -g
debug:  $(EXEC) $(TEXEC) 

obj/$(TGT)/%.o: %.c
        $(CC_68K) -c -o $@ $(INC_DIR) $<

thanks
adam t.