New symbols, to be overridden by configure.
(insn-*): Use $(md_file), not md.
(aux-output.o): Use $(out_file), not aux-output.c.
($(MD_FILE)): Rework to use new conventions.
(gen*.o, bi-*.o): Depend on $(build_xm_file), not hconfig.h.
(scan.o, fix-header.o, scan-decls.o): Likewise.
(distclean): Adjust files removed for new convention.

From jason@cygnus.com:
(STAGESTUFF): Add underscore.c.
(underscore.c): Rename temporary files to begin with 'tmp-' so that they will
be removed by 'make mostlyclean'.

From-SVN: r9608