posix: allow for external implementation of option groups

Make it easier for external C libraries, toolchains, and
integrators to override Zephyr's implementation of functions and
sybmols on a per-Option-Group basis.

This change adds a number of non-user-configurable Kconfig
options that block internal Cmake rules from building Zephyr's
C sources corresponding to the particular option.

This is useful, for example, if a specific C library has a smaller,
or faster, or more secure  version of some symbols belonging to a
a particular option group.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
3 files changed