allow CXXFLAGS to be set without overwriting needed flags

Makefile

@@ -17,7 +17,7 @@ i2p: $(OBJECTS:obj/%=obj/%)
 .SUFFIXES:	.c .cc .C .cpp .o
 
 obj/%.o : %.cpp
-	$(CXX) -o $@ $< -c $(CXXFLAGS) $(INCFLAGS) $(CPU_FLAGS)
+	$(CXX) -o $@ $< -c $(CXXFLAGS) $(NEEDED_CXXFLAGS) $(INCFLAGS) $(CPU_FLAGS)
 
 obj:
 	mkdir -p obj

Makefile.bsd

@@ -1,5 +1,6 @@
 CXX = g++
-CXXFLAGS = -std=c++11 -O2
+CXXFLAGS = -O2
+NEEDED_CXXFLAGS = -std=c++11
 include filelist.mk
 INCFLAGS = -I/usr/include/ -I/usr/local/include/
 LDFLAGS = -Wl,-rpath,/usr/local/lib -L/usr/local/lib -lcryptopp -lboost_system -lboost_date_time -lboost_filesystem -lboost_regex -lboost_program_options -lpthread

Makefile.linux

@@ -5,11 +5,11 @@ FGREP = fgrep
 IS_64 := $(shell $(CXX) -dumpmachine 2>&1 | $(FGREP) -c "64")
 
 ifeq ($(shell expr match ${CXXVER} "4\.[0-9][0-9]"),4) # >= 4.10
-CXXFLAGS += -std=c++11
+NEEDED_CXXFLAGS += -std=c++11
 else ifeq ($(shell expr match ${CXXVER} "4\.[7-9]"),3) # >= 4.7
-CXXFLAGS += -std=c++11
+NEEDED_CXXFLAGS += -std=c++11
 else ifeq ($(shell expr match ${CXXVER} "4\.6"),3) # = 4.6
-CXXFLAGS += -std=c++0x
+NEEDED_CXXFLAGS += -std=c++0x
 else # not supported
 $(error Compiler too old)
 endif