Makefile: rename GLUON_TARGETS to GLUON_TARGETLIST

Some communities are using GLUON_TARGETS as a variable in their makefile.
This can lead to conflicts when said variable is set on the commandline
by users of these communities' makefile.
This happened because this is just a temporary variable that was never
mentioned anywhere.

PR freifunk-gluon#2934

Makefile

@@ -111,11 +111,11 @@ update-modules: FORCE
 update-ci: FORCE
 	@$(GLUON_ENV) scripts/update-ci.sh
 
-GLUON_TARGETS :=
+GLUON_TARGETLIST :=
 
 define GluonTarget
 gluon_target := $(1)$$(if $(2),-$(2))
-GLUON_TARGETS += $$(gluon_target)
+GLUON_TARGETLIST += $$(gluon_target)
 GLUON_TARGET_$$(gluon_target)_BOARD := $(1)
 GLUON_TARGET_$$(gluon_target)_SUBTARGET := $(2)
 endef
@@ -132,7 +132,7 @@ SUBTARGET := $(GLUON_TARGET_$(GLUON_TARGET)_SUBTARGET)
 define CheckTarget
 	if [ -z '$(BOARD)' ]; then
 		echo 'Please set GLUON_TARGET to a valid target. Gluon supports the following targets:'
-		for target in $(GLUON_TARGETS); do
+		for target in $(GLUON_TARGETLIST); do
 			echo " * $$target"
 		done
 		exit 1
@@ -147,7 +147,7 @@ define CheckSite
 endef
 
 list-targets: FORCE
-	@for target in $(GLUON_TARGETS); do
+	@for target in $(GLUON_TARGETLIST); do
 		echo "$$target"
 	done
 
@@ -221,7 +221,7 @@ manifest: $(LUA) FORCE
 		echo "DATE=$$($(LUA) scripts/rfc3339date.lua)"
 		echo 'PRIORITY=$(GLUON_PRIORITY)'
 		echo
-		for target in $(GLUON_TARGETS); do
+		for target in $(GLUON_TARGETLIST); do
 			$(LUA) scripts/generate_manifest.lua "$$target"
 		done
 	) > 'tmp/$(GLUON_AUTOUPDATER_BRANCH).manifest.tmp'