* configure.host (sparc-*-netbsd): use sparcnbsd.

* configure.host (sparc-*-netbsd): use sparcnbsd.
  (ns32k-*-netbsd): use ns32knbsd.

* hosts/{nbsd,i386nbsd,ns32knbsd,sparcnbsd}.h: New files, NetBSD
  host support.

* sparcnetbsd.c: New file, adds support for NetBSD/sparc.
* config/sparc-nbsd.mt: Likewise.

* netbsd.h: New file, definitions common to all netbsd ports.
* i386netbsd.c: Use it.
* ns32knetbsd.c: Use it.

* Makefile.in, configure.in, targets.c, config/i386-nbsd.mt,
  config/ns32k-nbsd.mt: canonicalize netbsd targets to conform to
  file/variable naming conventions.
* i386netbsd.c: New file, renamed from netbsd386.c.
* ns32knetbsd.c: New file, renamed from netbsd532.c.