[build] Use variants

- Move helpers functions into build/helpers.mak
- Move official warning into official targets only

build/rules.mk

@@ -1,16 +1,5 @@
 # Define standard compilation rules
 
-.PHONY: official_authorization
-ifeq ($(ACCEPT_OFFICIAL_TOS),1)
-official_authorization:
-else
-official_authorization:
-	@echo "CAUTION: You are trying to build an official NumWorks firmware."
-	@echo "Distribution of such firmware by a third party is prohibited."
-	@echo "Please set the ACCEPT_OFFICIAL_TOS environment variable to proceed."
-	@exit -1
-endif
-
 $(eval $(call rule_for, \
   AS, %.o, %.s, \
   $$(CC) $$(SFLAGS) -c $$< -o $$@ \
@@ -22,12 +11,34 @@ $(eval $(call rule_for, \
   with_local_version \
 ))
 
+$(eval $(call rule_for, \
+  CPP, %, %.inc, \
+  $$(CPP) -P $$< $$@ \
+))
+
 $(eval $(call rule_for, \
   CXX, %.o, %.cpp, \
   $$(CXX) $$(CXXFLAGS) $$(SFLAGS) -c $$< -o $$@, \
   with_local_version \
 ))
 
+$(eval $(call rule_for, \
+  DFUSE, %.dfu, %.elf, \
+  $$(PYTHON) build/device/elf2dfu.py $$< $$@, \
+  with_local_version \
+))
+
+$(eval $(call rule_for, \
+  OBJCOPY, %.hex, %.elf, \
+  $$(OBJCOPY) -O ihex $$< $$@ \
+))
+
+$(eval $(call rule_for, \
+  OBJCOPY, %.bin, %.elf, \
+  $$(OBJCOPY) -O binary $$< $$@, \
+  with_local_version \
+))
+
 $(eval $(call rule_for, \
   OCC, %.o, %.m, \
   $$(CC) $$(CFLAGS) $$(SFLAGS) -c $$< -o $$@ \
@@ -39,8 +50,8 @@ $(eval $(call rule_for, \
 ))
 
 $(eval $(call rule_for, \
-  CPP, %, %.inc, \
-  $$(CPP) -P $$< $$@ \
+  WINDRES, %.o, %.rc, \
+  $$(WINDRES) $$< -O coff -o $$@ \
 ))
 
 ifdef EXE
@@ -61,8 +72,3 @@ $(eval $(call rule_for, \
 ))
 endif
 endif
-
-$(eval $(call rule_for, \
-  WINDRES, %.o, %.rc, \
-  $$(WINDRES) $$< -O coff -o $$@ \
-))