set CMAKE_SYSROOT variable

cmake/stm32/common.cmake

@@ -46,6 +46,8 @@ set(TOOLCHAIN_BIN_PATH "${STM32_TOOLCHAIN_PATH}/bin")
 set(TOOLCHAIN_INC_PATH "${STM32_TOOLCHAIN_PATH}/${STM32_TARGET_TRIPLET}/include")
 set(TOOLCHAIN_LIB_PATH "${STM32_TOOLCHAIN_PATH}/${STM32_TARGET_TRIPLET}/lib")
 
+set(CMAKE_SYSROOT ${TOOLCHAIN_SYSROOT})
+
 find_program(CMAKE_OBJCOPY NAMES ${STM32_TARGET_TRIPLET}-objcopy HINTS ${TOOLCHAIN_BIN_PATH})
 find_program(CMAKE_OBJDUMP NAMES ${STM32_TARGET_TRIPLET}-objdump HINTS ${TOOLCHAIN_BIN_PATH})
 find_program(CMAKE_SIZE NAMES ${STM32_TARGET_TRIPLET}-size HINTS ${TOOLCHAIN_BIN_PATH})