* configure.in (HAVE_MOTIF_2_1): Remove unused variable.
(LIBXP): No longer substitute in Makefiles.
(MOTIF_LIBW): New output variable. Move system-specific settings here
from src/s files.
* src/Makefile.in (LIBXP): Remove, since included in MOTIF_LIBW.
(MOTIF_LIBW): Set with configure, not cpp.
* s/aix4-2.h (LIB_MOTIF):
* s/gnu-linux.h (LIB_MOTIF):
* s/unixware.h (LIB_MOTIF): Move to configure.in.