Set FCFLAGS for CET support.

openmpi libraries built using Fortran lack CET support due to FCFLAGS not being set which is required to pass -fcf-protection to the Fortran compiler. Set FCFLAGS to the value of CFLAGS. Remove -Wformat -Werror=format-security from FCFLAGS which is not supported by gcc-fortran.

Fixes #2 (closed)