Including omp_lib module without -openmp flag breaks compilation with ifort

Fixes compilation error when OMP is not enable in configure:

$ mpiifort -O2 -assume byterecl -g -traceback -nomodule -fpp -allow nofpp_comments -D__DFTI -D__MPI -D__MPI_MODULE  -I/home/paulatto/espresso.request//external/devxlib/src -I. -I/home/paulatto/espresso.request//include -I/opt/intel/oneapi/mkl/2024.1/include  -c fft_parallel.f90
fft_parallel.f90(200): error #7002: Error in opening the compiled module file.  Check INCLUDE paths.   [OMP_LIB]
  USE omp_lib
------^