Introduce the first of the toolchain_cc-family of macros:
toolchain_cc_security_fortify and toolchain_cc_security_canaries.
No functional change expected.
Fortify source is not supported by Clang, but this commit retains
current behavior.
This is motivated by the wish to abstract Zephyr's usage of toolchains,
permitting easier porting to other (commercial) toolchains.
Signed-off-by: Mark Ruvald Pedersen <mped@oticon.com>