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.
(which is not a Posix signal) if it isn't defined.
* tm-linux.h, xm-linux.h, config/linux.m[ht], configure.in:
New port to Linux (a free Unix clone for 386 machines).