Change default compiler for regional_Greece_small

In the script run_this_example.sh, the code was configured with

./configure F90=ifort MPIF90=/usr/local/openmpi-ifort/bin/mpif90 \
 FLAGS_CHECK="-O3 -assume byterecl" > tmp.log

by default. This is a not a standard setting. And it causes some issues
with running the buildbot test.

This commit sets the default to the GNU compilers.
Ignore constants_tomography.h file.
Remove some unused variables.

They're set, but not used for anything.
Move variable from module to subroutine.

It's only used in one subroutine and even then for some really small
portion.
updates configure scripts to match also SPECFEM3D_Cartesian ones
updates smoothing, interpolation; makes difference_sem to work in parallel
adds tool addition_sem to src/tomography
fixes filename argument for routine write_kernel_netcdf()
"Buildbot ran code beautifier."
suppressed the "configure" and "make" steps from all the run_this_example.sh