The texlive package uses ../configure rather than %configure which means when distro cflags are changed the package doesn't automatically benefit You can still use %configure from a different directory. An example of how to do so is: http://pkgs.fedoraproject.org/cgit/nspr.git/commit/?id=c03a2a6b62ab5615af44ff25430e950f00587fdc
This is fixed in rawhide (texlive-2015-16.20150728_r37987.fc24).