add few more missing gnulib modules

Along with other necessary changes to gain better portability.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
fix compiler warning

f5gs.c:259:1: warning: embedding a directive within macro arguments is
not portable [enabled by default]

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
remove unnecessary variables and use as narrow scope as possible

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
fail when command is ran with excess arguments

Signed-off-by: Sami Kerola <kerolasa@iki.fi>