posix: disable clang-format where checkpatch disagrees

checkpatch and clang-format have conflicting formatting requirements for
this file for whatever reason.

Since it is not possible to selectively disable checkpatch, but it is
possible to selectively disable clang-format, disable clang-format
surrounding some macros in `posix_features.h` and `sys/sysconf.h` in order
to eliminate linter noise.

The code is still checked by checkpatch, which should be sufficient.

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