Remove -Wsign-conversion for the moment

This warning option causes a flood of warnings in third party components,
so other warnings are no longer visible in the many pages of warnings.
For the moment remove this option again.
Later it could be activated for CivetWeb without the third_party folder.

Makefile

@@ -60,7 +60,7 @@ BUILD_DIRS += $(BUILD_DIR)/test
 endif
 
 # only set main compile options if none were chosen
-CFLAGS += -Wall -Wextra -Wshadow -Wformat-security -Winit-self -Wmissing-prototypes -Wsign-conversion -O2 -D$(TARGET_OS) -Iinclude $(COPT) -DUSE_STACK_SIZE=102400
+CFLAGS += -Wall -Wextra -Wshadow -Wformat-security -Winit-self -Wmissing-prototypes -O2 -D$(TARGET_OS) -Iinclude $(COPT) -DUSE_STACK_SIZE=102400
 
 LIBS = -lpthread -lm