pcre on OS X

Not sure of this has already been discussed. There is now a libpcre
sitting in /usr/lib (OS X 10.12.4) and R-devel does not like
that version. So I had to use LDFLAGS to link with the pcre from 
homebrew if I wanted the build to finish.

=================================================================
Jan de Leeuw, Distinguished Professor Emeritus, UCLA Statistics
http://gifi.stat.ucla.edu ? https://www.facebook.com/jan.deleeuw1
=================================================================
             The Good -- and this is surely true -- 
             is just the Bad that we don't do !     (Wilhelm Busch)