BUILD: makefile: move common options-oriented macros to include/make/options.mk

Some macros and functions are barely understandable and are only used
to iterate over known options from the use_opts list. Better assign
them a name and move them into a dedicated file to clean the makefile
a little bit. Now at least "use_opts" only appears once, where it is
defined. This also allowed to completely remove the BUILD_FEATURES
macro that caused some confusion until previous commit.
2 files changed