Merge of r4961: configure: better check for PCRE JIT. 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 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.