prewarm compiler warnings

gcc-6.3.0 complains about this:

autoprewarm.c: In function ‘autoprewarm_main’:
autoprewarm.c:210:9: warning: variable ‘rc’ set but not used
[-Wunused-but-set-variable]
int rc;

The warning comes only in master.

The warnings are a bit annoying; the attached silences them by removing
those assignments.

Thanks,

Erik Rijkers