cmake: Toolchain abstraction: Introduce macros for MISRA SANE flags

The macros are named toolchain_cc_warning_error_misra_sane and
toolchain_cc_cpp_warning_error_misra_sane

These macros provide toolchain specific flag(s) relating to the MISRA
SANE configuration option.
The macros will place the flag(s) in a variable provided by caller,
which can then add to zephyr compile options.

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>