inkscape 0.92.1-3.20170321bzr15604 is not built with $RPM_OPT_FLAGS. Quite likely changing /usr/bin/cmake to %cmake (and dropping redundant options) would fix the problem. Some care will probably be needed in handling of the -NDEBUG option so it won't end up overwriting desired CFLAGS etc. 0.92.1-1 did not have this issue.
inkscape-0.92.1-4.20170510bzr15686.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2017-5f9d9f1c90
inkscape-0.92.1-4.20170510bzr15686.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-b90b5f6b40
inkscape-0.92.1-4.20170510bzr15686.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-5f9d9f1c90
inkscape-0.92.1-4.20170510bzr15686.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-b90b5f6b40
inkscape-0.92.1-4.20170510bzr15686.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.
inkscape-0.92.1-4.20170510bzr15686.fc25 has been pushed to the Fedora 25 stable repository. If problems still persist, please make note of it in this bug report.