Organize codegen source files and unit tests
Organize codegen source files and unit tests

* Move these into one gpcodegen dynamic library, leaving on
  codegen_wrapper.cc in SUBSYS.o
* Convert simple-gtests to cmockery_gtests since libgpcodegen may have
  references to Postgres symbols

Minor changes

adam8157/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,lintzc/gpdb,cjcjameson/gpdb,edespino/gpdb,lintzc/gpdb,kaknikhil/gpdb,adam8157/gpdb,Chibin/gpdb,cjcjameson/gpdb,xinzweb/gpdb,cjcjameson/gpdb,lintzc/gpdb,janebeckman/gpdb,yuanzhao/gpdb,Chibin/gpdb,Quikling/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,rvs/gpdb,lisakowen/gpdb,greenplum-db/gpdb,Chibin/gpdb,janebeckman/gpdb,adam8157/gpdb,Quikling/gpdb,lisakowen/gpdb,Chibin/gpdb,kaknikhil/gpdb,rvs/gpdb,jmcatamney/gpdb,edespino/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,lintzc/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,edespino/gpdb,rvs/gpdb,yuanzhao/gpdb,janebeckman/gpdb,Quikling/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,Chibin/gpdb,Chibin/gpdb,adam8157/gpdb,cjcjameson/gpdb,50wu/gpdb,rvs/gpdb,janebeckman/gpdb,kaknikhil/gpdb,xinzweb/gpdb,cjcjameson/gpdb,xinzweb/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,rvs/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,Chibin/gpdb,50wu/gpdb,Chibin/gpdb,adam8157/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,edespino/gpdb,Quikling/gpdb,lisakowen/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,janebeckman/gpdb,yuanzhao/gpdb,xinzweb/gpdb,edespino/gpdb,Quikling/gpdb,edespino/gpdb,janebeckman/gpdb,janebeckman/gpdb,edespino/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,lintzc/gpdb,yuanzhao/gpdb,Chibin/gpdb,50wu/gpdb,lintzc/gpdb,cjcjameson/gpdb,xinzweb/gpdb,lintzc/gpdb,rvs/gpdb,cjcjameson/gpdb,rvs/gpdb,janebeckman/gpdb,Quikling/gpdb,janebeckman/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,Quikling/gpdb,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,janebeckman/gpdb,xinzweb/gpdb,yuanzhao/gpdb,Quikling/gpdb,rvs/gpdb,Quikling/gpdb,ashwinstar/gpdb,edespino/gpdb,50wu/gpdb,jmcatamney/gpdb,rvs/gpdb,yuanzhao/gpdb,edespino/gpdb,adam8157/gpdb,Chibin/gpdb,Quikling/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,lintzc/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,rvs/gpdb,lintzc/gpdb,edespino/gpdb,jmcatamney/gpdb,adam8157/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,50wu/gpdb