On Mac OS X system toolchain by default prefers include files
from /usr/local/include, but libraries from /usr/lib. This might result in
various problems, in particular the one outlined below.
If the PCRE library is installed into /usr/local/, this results in pcre.h
being used from /usr/local/include (with PCRE_CONFIG_JIT defined), but
libpcre from /usr/lib (as shipped with the OS, without pcre_free_study()
symbol). As a result build fails as we use pcre_free_study() function
if we try to compile with PCRE JIT support.
Obvious workaround is to the root cause is to ask compiler to prefer
library from /usr/local/lib via ./configure --with-ld-opt="-L/usr/local/lib".
On the other hand, in any case it would be good to check if the function
we are going to use is available, hence the change.
See thread here for details:
http://mailman.nginx.org/pipermail/nginx-devel/2012-December/003074.html
Prodded by Piotr Sikora.