Build system: Add a few -Werror for sane C development

Makefile

@@ -236,7 +236,10 @@ tag: distcheck
 .SECONDARY:
 
 cflags := $(CPPFLAGS) -I$(SRCDIR)src
-cflags += -std=gnu99 $(CFLAGS)
+cflags += -std=gnu99 $(CFLAGS) \
+	-Werror=incompatible-pointer-types \
+	-Werror=implicit-function-declaration \
+	-Werror=int-conversion
 %.o: %.c
 	@test -d $(@D) || $(MKDIR) $(@D)
 	$(CC) $(cflags) $($(basename $(notdir $@))_CCFLAGS) -c -o $@ $<

src/tinycbor.pro

@@ -1,6 +1,10 @@
 TEMPLATE = lib
-CONFIG += static
+CONFIG += static warn_on
 CONFIG -= qt
 DESTDIR = ../lib
 
+!msvc:QMAKE_CFLAGS += \
+    -Werror=incompatible-pointer-types \
+    -Werror=implicit-function-declaration \
+    -Werror=int-conversion
 include(src.pri)