cmake: Toolchain abstraction: Introducing macro toolchain_cc_cstd_flag

The macro obtains the toolchain specific flag and value for
setting of the requested c standard.

The intent here is to abstract Zephyr's dependence on toolchains,
thus allowing for easier porting to other, perhaps commercial,
toolchains and/or usecases.

No functional change expected.

Signed-off-by: Danny Oerndrup <daor@demant.com>
2 files changed