Comment 14 for bug 93603

As far as I can see, there's no issue at all with GMP. Certainly, nothing is mentioned about a license clash here:
   http://www.php.net/manual/en/ref.gmp.php
(My understanding is that LGPL code can be linked with anything, even non-free software).

As for Readline, you can build the readline extension with either gnu-readline (GPL), or libedit (BSD).
   http://www.php.net/manual/en/ref.readline.php
I'm still confused as to exactly how this is incompatible - surely the extension would never have been written if it were incompatible in this way.
Also, Mandriva (who are usually pretty strict about licensing) ship both of these; so do Fedora and Suse.