%perl56 Makefile.PL PREFIX=/tmp/test INSTALLDIRS=perl
%make
%make install

and
use lib qw(/tmp/test/lib);

If you don't set INSTALLDIRS, the modules go to /tmp/test/lib/site_perl, so you need
use lib qw(/tmp/test/lib/site_perl);

perl56 Makefile.PL PREFIX=/path/to/install/grib/api INSTALLDIRS=perl

perl Makefile.PL PREFIX=/path/to/install/grib/api INSTALLDIRS=perl LD="ld -b32"
