modules: hal_rpi_pico: set -std=gnu11 in a toolchain independent way.

Set `-std=gnu11` in a more toolchain independent way.

Signed-off-by: Robin Kastberg <[email protected]>

Author: RobinKastberg

modules/hal_rpi_pico/CMakeLists.txt

@@ -4,7 +4,7 @@ include(ExternalProject)
 
 if(CONFIG_HAS_RPI_PICO)
   zephyr_library()
-  zephyr_library_compile_options(-std=gnu11)
+  set_property(TARGET ${ZEPHYR_CURRENT_LIBRARY} PROPERTY C_STANDARD 11)
 
   set(rp2_common_dir ${ZEPHYR_HAL_RPI_PICO_MODULE_DIR}/src/rp2_common)
   set(rp2xxx_dir ${ZEPHYR_HAL_RPI_PICO_MODULE_DIR}/src/${CONFIG_SOC_SERIES})