New Build System... move common stuff to xpdev/Common.gmake

src/sbbs3/GNUmakefile

src/sbbs3/install/GNUmakefile

src/sbbs3/install/objects.mk

src/sbbs3/install/targets.mk

src/sbbs3/scfg/GNUmakefile

src/sbbs3/scfg/objects.mk

src/sbbs3/scfg/targets.mk

src/sbbs3/targets.mk

src/sbbs3/uedit/GNUmakefile

src/sbbs3/umonitor/GNUmakefile

src/xpdev/Common.gmake

src/xpdev/GNUmakefile

src/xpdev/objects.mk

src/xpdev/targets.mk