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.
diff --git a/include/make/options.mk b/include/make/options.mk
new file mode 100644
index 0000000..4179e9a
--- /dev/null
+++ b/include/make/options.mk
@@ -0,0 +1,33 @@
+# this contains various functions and macros used to manipulate USE_* options
+# and their flags
+
+# Depending on the target platform, some options are set, as well as some
+# CFLAGS and LDFLAGS. All variables pre-set here will not appear in the build
+# options string. They may be set to any value, but are historically set to
+# "implicit" which eases debugging. You should not have to change anything
+# there unless you're adding support for a new platform.
+default_opts = $(foreach name,$(1),$(eval $(name)=implicit))
+
+# Return USE_xxx=$(USE_xxx) if the variable was set from the environment or the
+# command line.
+ignore_implicit = $(if $(subst environment,,$(origin $(1))), \
+ $(if $(subst command line,,$(origin $(1))),, \
+ $(1)=$($(1))), \
+ $(1)=$($(1))) \
+
+# This macro collects all USE_* values except those set to "implicit". This
+# is used to report a list of all flags which were used to build this version.
+# Do not assign anything to it.
+build_options = $(foreach opt,$(use_opts),$(call ignore_implicit,$(opt)))
+
+# Make a list of all known features with +/- prepended depending on their
+# activation status. Must be a macro so that dynamically enabled ones are
+# evaluated with their current status.
+build_features = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),+$(opt),-$(opt)))
+
+# This returns a list of -DUSE_* for all known USE_* that are set
+opts_as_defines = $(foreach opt,$(use_opts),$(if $($(opt)),-D$(opt),))
+
+# Lists all enabled or disabled options without the "USE_" prefix
+enabled_opts = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),$(opt),))
+disabled_opts = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),,$(opt)))