respect CFLAGS: should I override optimizations?

[Roman Neuhauser]

I'm updating biology/migrate, the upstream Makefile.in includes

CFLAGS = @CFLAGS@ ...

and configure says:

case "$GCC" in
	yes) CFLAGS="-O3 -Wall -ffast-math -funroll-loops -fomit-frame-pointer -fexpensive-optimizations -D$CPUTYPE" ;;
 
If I was to take Porter's Hang^Hdbook literally, I would change the
set (=) to append (+=) and be done with it, but is that really what
I'm expected to do? Or should I filter out the -O3 on the assumption
that optimization levels are make.conf's business?

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