* mcheck.c: Avoid warning about undeclared abort fn.

* mcheck.c:  Avoid warning about undeclared abort fn.
* tm-sparc.h (PC_ADJUST):  Avoid calling error() from this;
it causes recursive calls to error() when used in cleanups.
To do so requires that we make it a function, so we do.
* sparc-tdep.c (sparc_pc_adjust):  New implem of PC_ADJUST.
* utils.c (do_cleanups):  Remove the current cleanup from the
chain *before* calling it, in case error() is called from it.
The result won't be pretty, but won't be an infinite loop either.