bug#16757: [PATCH 1/2] search for pcre via pkg-config

[Paul Eggert]

Thanks for the patch in <http://bugs.gnu.org/16757>.  In looking it over 
I see a couple of things.  First, it looks big enough that we'll need 
copyright papers for it.  Can you please get the ball rolling on that? 
I assume you know the drill.

Second, doesn't this patch create a dependency on pkg-config, in the 
sense that if one checks out 'grep' from git, one needs pkg-config to 
build grep?  If so, that should be added to the README-prereq file.