Use system include directories

Currently all include directories are added as none system include directories. This might causes warnings and errors when compiling user code.

Author: ooxi

src/CMakeLists.txt

@@ -102,7 +102,7 @@ macro(pico_simple_hardware_headers_target NAME)
     if (NOT TARGET hardware_${NAME}_headers)
         add_library(hardware_${NAME}_headers INTERFACE)
 
-        target_include_directories(hardware_${NAME}_headers INTERFACE ${CMAKE_CURRENT_LIST_DIR}/include)
+        target_include_directories(hardware_${NAME}_headers SYSTEM INTERFACE ${CMAKE_CURRENT_LIST_DIR}/include)
         target_link_libraries(hardware_${NAME}_headers INTERFACE pico_base_headers)
         if (NOT PICO_NO_HARDWARE)
             target_link_libraries(hardware_${NAME}_headers INTERFACE hardware_structs hardware_claim_headers)

src/common/pico_base/CMakeLists.txt

@@ -1,6 +1,6 @@
 if (NOT TARGET pico_base_headers)
     pico_add_library(pico_base NOFLAG)
-    target_include_directories(pico_base_headers INTERFACE include ${CMAKE_BINARY_DIR}/generated/pico_base)
+    target_include_directories(pico_base_headers SYSTEM INTERFACE include ${CMAKE_BINARY_DIR}/generated/pico_base)
 
     # PICO_BUILD_DEFINE: PICO_BOARD, Name of board, type=string, default=CMake PICO_BOARD variable, group=pico_base
     target_compile_definitions(pico_base_headers INTERFACE
@@ -10,4 +10,4 @@ if (NOT TARGET pico_base_headers)
 
     list(APPEND PICO_SDK_POST_LIST_FILES ${CMAKE_CURRENT_LIST_DIR}/generate_config_header.cmake)
     pico_promote_common_scope_vars()
-endif()
+endif()