(gud-mips-p, gud-irix-p): Test system-configuration.

(gud-mips-p, gud-irix-p): Test system-configuration.

(gud-mipsdbx-marker-filter): Reimplemented based on
gud-gdb-marker-filter, with regexps appropriately altered.
(gud-marker-acc): New variable, replacing the
debugger-specific accumulation variables.
(dbx): Arrange to fire up the source window with irixdbx.

(dbx): Fix gud-break under SunOS, at least.  (I suspect
this is a general problem, because of the \n for some reason.)

(gud-dbx-mips-p, gud-dbx-irix-p): Use system-type to
choose system-dependent dbx incantations.

(gud-dbx-mips-p): Use "-emacs" for OSF/1 dbx as for MIPS.

(gud-irix-dbx-p): Determines whether to use (new) gud-irixdbx-marker-filter.
(gud-irixdbx-marker-filter): New function.
(dbx): Insert case for Irix.