This was adequate for my needs:

MAKEALL := $(findstring B,$(MAKEFLAGS))

DRYRUN := $(findstring n,$(MAKEFLAGS))

Picks off two make option flags:

@echo "MAKEFLAGS: $(MAKEFLAGS) MAKEALL: $(MAKEALL) DRYRUN: $(DRYRUN)"

Result:

make -Bi

MAKEFLAGS: Bi MAKEALL: B DRYRUN:

Thus these flags can be tested for individually.