Exclude common/int128.h from cpluspluscheck
Exclude common/int128.h from cpluspluscheck

It uses static assertions, which are not supported under C++ in this
branch.

This change only goes into the 9.4 branch, because 9.5 and beyond will
primarily use the USE_NATIVE_INT128 branch, so cpluspluscheck isn't
bothered.  In PG11 we will have C++ support for static assertions, so
the issue will go away altogether.

greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb