maint: reformat for consistency and GNU style function headers.

* ext/posix/posix.c: Put function return types on a separate
line for easy function name grepping; don't use cuddle braces;
indent case branches one tab; exdent labels one tab; don't put a
space between function call and arguments; do put a space between
flow control keyword and arguments.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>