suppress error with net example

examples/device/net_lwip_webserver/CMakeLists.txt

@@ -76,6 +76,8 @@ if (EXISTS ${TOP}/lib/lwip/src)
     target_compile_options(${PROJECT} PUBLIC
         -Wno-error=null-dereference
         -Wno-error=conversion
+        -Wno-error=sign-conversion
+        -Wno-error=sign-compare
         )
 
     # Configure compilation flags and libraries for the example... see the corresponding function

examples/make.mk

@@ -113,7 +113,8 @@ CFLAGS += \
   -Wunused \
   -Wredundant-decls
 
-#  -Wconversion \
+# conversion is too strict for most mcu driver, may be disable sign/int/arith-conversion
+#  -Wconversion
   
 # Debugging/Optimization
 ifeq ($(DEBUG), 1)