Previous versions
$ echo "==$(pkg-config --cflags-only-I openssl)==" == ==
New version $ echo "==$(pkg-config --cflags-only-I openssl)==" ====
This space to empty string output can breaks some poorly written autoconf script.
Remi.
P.S.1: I hope it could helps some packager... avoid losing too much time on this... P.S.2: example of broken script http://git.php.net/?p=php-src.git;a=commitdiff;h=640e72ce91d8e591b92cd93c18d...