Bug 612340 - [Patch] Add missing libm & libX11 linking

XChat-GNOME fails to build due to a change DSO-linking semantics of the gcc
compiler in Fedora. For more info please refer to:
https://bugzilla.redhat.com/show_bug.cgi?id=564820
http://fedoraproject.org/wiki/Features/ChangeInImplicitDSOLinking
http://fedoraproject.org/wiki/UnderstandingDSOLinkChange