get linked to nm.h, xm.h, and tm.h respectively by configure,
moved to appropriate config/<cpu> subdirectory.
* nm-sysv4.h, xm-sysv4.h, tm-sysv4.h, tm-sunos.h, nm-trash.h:
Native, host, and target files that are common across more than
one cpu architecture and included by one of the configured
native, host, or target files, get moved to config directory.
* nat-sparc.c -> sparc-nat.c
* nat-sun4os4.h -> nm-sun4os4.h
* nat-trash.h -> nm-trash.h
* configure.in: link to nm.h rather than nat.h.
* infptrace.c: include nm.h rather than nat.h.