Libiberty/alloca patch: fix giant memory leak in fixincl/gnu-regex

[DJ Delorie]

Since the *only* place I could find this macro used in all the sources
on gcc.gnu.org or sources.redhat.com is GNU regex, yes, OK to install.

I wish we had libiberty documentation so I could add "don't forget to
document it" ;)

> Ok to install?
> 
> 2001-03-29  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
> 
> 	* libiberty.h (alloca): Handle setting C_ALLOCA.