Incorrect compiler options on AIX with GCC

[merlinscholz]

When trying to compile DBD::DB2 on AIX with GCC, I ran into gcc: error: unrecognized command-line option '-qcpluscmt'.

This is a XLC-exclusive flag and seems to be caused by https://github.com/ibmdb/perl_DBD-DB2/blob/master/Constants/Makefile.PL#L79, which assumes that XLC is the only compiler used on AIX. After commenting out the line that tries to add the -qcpluscmt flag on AIX, the compilation works fine (with GCC).

My suggestion would be to only add this flag when used in combination with XLC, not on AIX in general.