Clean up warnings

* Use -Wall -Wextra -Wformat -Wformat-security -Wno-unused-parameters
* Remove xCXXFLAGS usage in makefile.unix
* Fix several recent and older sign-compare warnings

src/makefile.unix

@@ -82,9 +82,8 @@ LIBS+= \
 
 
 DEBUGFLAGS=-g
-CXXFLAGS=-O2
-xCXXFLAGS=-pthread -Wall -Wextra -Wno-invalid-offsetof -Wno-unused-parameter -Wformat -Wformat-security \
-    $(DEBUGFLAGS) $(DEFS) $(HARDENING) $(CXXFLAGS)
+CXXFLAGS=-O2 -pthread -Wall -Wextra -Wformat -Wformat-security -Wno-unused-parameter \
+    $(DEBUGFLAGS) $(DEFS) $(HARDENING)
 
 OBJS= \
     obj/version.o \
@@ -121,26 +120,26 @@ version.cpp: obj/build.h
 DEFS += -DHAVE_BUILD_INFO
 
 obj/%.o: %.cpp
-	$(CXX) -c $(xCXXFLAGS) -MMD -o $@ $<
+	$(CXX) -c $(CXXFLAGS) -MMD -o $@ $<
 	@cp $(@:%.o=%.d) $(@:%.o=%.P); \
 	  sed -e 's/#.*//' -e 's/^[^:]*: *//' -e 's/ *\\$$//' \
 	      -e '/^$$/ d' -e 's/$$/ :/' < $(@:%.o=%.d) >> $(@:%.o=%.P); \
 	  rm -f $(@:%.o=%.d)
 
 bitcoind: $(OBJS:obj/%=obj/%)
-	$(CXX) $(xCXXFLAGS) -o $@ $^ $(LDFLAGS) $(LIBS)
+	$(CXX) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) $(LIBS)
 
 TESTOBJS := $(patsubst test/%.cpp,obj-test/%.o,$(wildcard test/*.cpp))
 
 obj-test/%.o: test/%.cpp
-	$(CXX) -c $(TESTDEFS) $(xCXXFLAGS) -MMD -o $@ $<
+	$(CXX) -c $(TESTDEFS) $(CXXFLAGS) -MMD -o $@ $<
 	@cp $(@:%.o=%.d) $(@:%.o=%.P); \
 	  sed -e 's/#.*//' -e 's/^[^:]*: *//' -e 's/ *\\$$//' \
 	      -e '/^$$/ d' -e 's/$$/ :/' < $(@:%.o=%.d) >> $(@:%.o=%.P); \
 	  rm -f $(@:%.o=%.d)
 
 test_bitcoin: $(TESTOBJS) $(filter-out obj/init.o,$(OBJS:obj/%=obj/%))
-	$(CXX) $(xCXXFLAGS) -o $@ $(LIBPATHS) $^ -Wl,-B$(LMODE) -lboost_unit_test_framework $(LDFLAGS) $(LIBS)
+	$(CXX) $(CXXFLAGS) -o $@ $(LIBPATHS) $^ -Wl,-B$(LMODE) -lboost_unit_test_framework $(LDFLAGS) $(LIBS)
 
 clean:
 	-rm -f bitcoind test_bitcoin