[PATCH] Outwit compiler dead code elimination in break.exp test

[Fred Fish]

> 	* gdb.base/break.c (globalvar): Add.
> 	(marker1, marker2, marker3, marker4): Set globalvar.

BTW, as it turns out this breaks some other tests that depend upon
hardwired line numbers into break.c, so I'm updating those.  If
nothing else, it might be a good idea to mark those lines that do have
hardwired line numbers to make them easier to find again in the
future.

-Fred