Create mapping to most of the C spec and some POSIX specific functions.
This is more robust than relying files shipped with IWYU.

This requires removing the "Inner expression should be aligned" rule
from clint as it prevents essentially any formatting regarding ternary
operators.

It is less error-prone than manually defining header guards. Pretty much
all compilers support it even if it's not part of the C standard.

We already have an extensive suite of static analysis tools we use,
which causes a fair bit of redundancy as we get duplicate warnings. PVS
is also prone to give false warnings which creates a lot of work to
identify and disable.