Fix compatibility with GCC 4.8

Closes #2045

extras/CompileOptions.cmake

@@ -32,8 +32,18 @@ endif()
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
 	if((CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 4.8) AND(NOT ${COVERAGE}))
 		add_compile_options(-g -Og)
-	else()
-		add_compile_options(-g -O0)
+	else() # GCC 4.8
+		add_compile_options(
+			-g
+			-O0 # GCC 4.8 doesn't support -Og
+			-Wno-shadow  # allow the same name for a function parameter and a member functions
+			-Wp,-w  # Disable preprocessing warnings (see below)
+		)
+		# GCC 4.8 doesn't support __has_include, so we need to help him
+		add_definitions(
+			-DARDUINOJSON_ENABLE_STD_STRING=1
+			-DARDUINOJSON_ENABLE_STD_STREAM=1
+		)
 	endif()
 
 	add_compile_options(