If the compiler complains about invalid syntax related to config.h,
the most likely origin of the problem is an incorrect default setting of the
preprocessor options in the config file of xlf, explicitely asking to
leave C comments in the preprocessed file.
This is solved by editing xlf.cfg, replacing:
cppoptions = -C
by:
cppoptions = -P
If you do not have write permissions on this file, then copy it into
your home directory before modifying it. It is usually located in /etc
or /etc/opt/ibmcmp/xlf/<version>.
You will also need either to reconfigure Abinit the following way:
../configure FC="xlf -F /path/to/xlf.cfg"
or to force make to use the modified compiler:
make FC="xlf -F /path/to/xlf.cfg"
Of course, do not hesitate to replace xlf by any other name if needed,
e.g. mpif90.
If make succeed, you should probably consider asking your system
administrator to edit the system-wide config file or create another one.