include PDFLIB_SHARED_LIBADD in the pdflib test, or it fails with

unresolved symbols on OpenBSD

ext/pdf/config.m4

@@ -111,7 +111,7 @@ Use the options --with-tiff-dir=<DIR>, --with-jpeg-dir=<DIR>, --with-png-dir=<DI
 See config.log for more information.
 ])
         ],[
-          -L$PHP_PDFLIB/lib
+          -L$PHP_PDFLIB/lib $PDFLIB_SHARED_LIBADD
         ])
       else
         AC_MSG_ERROR([pdflib.h not found! Check the path passed to --with-pdflib=<PATH>. PATH should be the install prefix directory.])