There were a few places where the texinfo variables GDBP, GDBN, and GCC were not 
used.

OK?

2007-03-23  Bob Wilson  <bob.wilson@acm.org>
	
	* gdb.texinfo (Invoking GDB): Use @value{GDBP}.
	(Source Path, Character Sets, Macros, Define)
	(GDB/MI Result Records, GDB/MI Simple Examples)
	(GDB/MI Program Execution, GDB/MI File Commands)
	(Maintenance Commands, Packets, File-I/O Overview): Use @value{GDBN}.
	(Bug Reporting): Use @value{GCC}.