[makefile] Make error: missing separator

Just to add yet another reason this can show up:

$(eval VALUE)

is not valid and will produce a "missing separator" error.

$(eval IDENTIFIER=VALUE)

is acceptable. This sort of error showed up for me when I had an macro defined with define and tried to do

define SOME_MACRO
... some expression ...
endef

VAR=$(eval $(call SOME_MACRO,arg))

where the macro did not evaluate to an assignment.