posix: getopt: move declarations to unistd.h

Declarations for `getopt()` should be in `<unistd.h>`
according to the spec. The extended versions `getopt_long()`
and `getopt_long_only()` are declared in `<getopt.h>`.

Signed-off-by: Chris Friedt <cfriedt@meta.com>
5 files changed