cmake: add -Wall/-Wshadow to GCC compilation flags

CMakeLists.txt

@@ -331,11 +331,15 @@ if(USE_GCC OR USE_CLANG)
 
   check_c_compiler_flag(-Wall HAVE_GCC_WALL)
   if(HAVE_GCC_WALL)
+    list(APPEND EXTRA_CFLAGS "-Wall")
     if(HAIKU)
       set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-multichar")
     endif()
   endif()
-  #check_c_compiler_flag(-Wshadow HAVE_GCC_WSHADOW)
+  check_c_compiler_flag(-Wshadow HAVE_GCC_WSHADOW)
+  if(HAVE_GCC_WSHADOW)
+    list(APPEND EXTRA_CFLAGS "-Wshadow")
+  endif()
 endif()
 
 if(ASSEMBLY)