Adjust GD32 firmware warning flags

Refactors GD32 firmware warning options into incremental assignments, adds additional non-fatal warning suppressions, and wires those flags into the GD32 firmware-template C compile rule. Also adds `-Dcplusplus` to shared C++ options to ensure that define is consistently available during builds.

Author: vanvught

common/make/CppOps.mk

@@ -4,4 +4,5 @@ CPPOPS=-std=c++20
 CPPOPS+=-Wnon-virtual-dtor -Woverloaded-virtual -Wnull-dereference -fno-rtti -fno-exceptions -fno-unwind-tables
 CPPOPS+=-Wuseless-cast -Wold-style-cast
 CPPOPS+=-fno-threadsafe-statics -fno-use-cxa-atexit
-CPPOPS+=-Wshadow -Wshadow=local
+CPPOPS+=-Wshadow -Wshadow=local
+CPPOPS+=-Dcplusplus

common/make/gd32/Gd32FirmwareOps.mk

@@ -1,3 +1,9 @@
 $(info "Gd32FirmwareOpts.mk")
 
-GD32FIRMWAREOPS=-Wno-error=unused-parameter -Wno-error=unused-but-set-variable -Wno-error=conversion -Wno-error=old-style-cast
+GD32FIRMWAREOPS =-Wno-error=unused-parameter 
+GD32FIRMWAREOPS+=-Wno-error=unused-but-set-variable 
+GD32FIRMWAREOPS+=-Wno-error=conversion
+GD32FIRMWAREOPS+=-Wno-error=old-style-cast
+GD32FIRMWAREOPS+=-Wno-error=unused-function
+GD32FIRMWAREOPS+=-Wno-error=unused-variable
+GD32FIRMWAREOPS+=-Wno-error=duplicated-cond

firmware-template-gd32/lib/Rules.mk

@@ -39,6 +39,7 @@ COPS+=-Wconversion
 endif
 
 include ../common/make/CppOps.mk
+include ../common/make/gd32/Gd32FirmwareOps.mk
 
 BUILD=build_gd32/
 BUILD_DIRS:=$(addprefix build_gd32/,$(SRCDIR))
@@ -60,7 +61,7 @@ $(info $$TARGET [${TARGET}])
 define compile-objects
 $(info $1)
 $(BUILD)$1/%.o: $1/%.c
-	$(CC) -MD -MP $(COPS) -c $$< -o $$@
+	$(CC) -MD -MP $(COPS) $(GD32FIRMWAREOPS) -c $$< -o $$@
 
 $(BUILD)$1/%.o: $1/%.cpp
 	$(CPP) -MD -MP $(COPS) $(CPPOPS) -c $$< -o $$@