Avoid use of gets() in DOE-ProxyApps-C/Pathfinder

gets() has been removed from C11 and on FreeBSD 13 libc no longer provides
it by default. Use fgets() instead.

Reviewed By: arichardson

Differential Revision: https://reviews.llvm.org/D89556

(cherry picked from commit ad49cd738e93f77b86bae2ac6a127ed886427d25)
1 file changed