Not sure how the flags should be applied to D apps, but 1.5.4-4 was built with -g in them (yet missing all other standard optflags), and its debuginfo package contains sources, unlike the 1.5.6-1 one.
Looks like a regression from upstream commit https://github.com/gnunn1/tilix/commit/83b9aabd90ec4b4c34047e28c448d5a690152b13 which makes the build process ignore Fedora supplied DCFLAGS
Should be fixed in tilix-1.6.1-1.fc26
avgtime-0.5.1-0.7.git20150501.fc26 dustmite-1-31.20150515git3498068.fc26 derelict-3-39.20150730git10a517b.fc26 gl3n-1.3.1-4.fc26 gtkd-3.6.5-1.fc26 tilix-1.6.1-1.fc26 ldc-1.3.0-0.3.beta2.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-d0471dcfcb
avgtime-0.5.1-0.7.git20150501.fc26, derelict-3-39.20150730git10a517b.fc26, dustmite-1-31.20150515git3498068.fc26, gl3n-1.3.1-4.fc26, gtkd-3.6.5-1.fc26, ldc-1.3.0-0.4.beta2.fc26, tilix-1.6.1-1.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-d0471dcfcb
avgtime-0.5.1-0.7.git20150501.fc26, derelict-3-39.20150730git10a517b.fc26, dustmite-1-31.20150515git3498068.fc26, gl3n-1.3.1-4.fc26, gtkd-3.6.5-1.fc26, ldc-1.3.0-0.4.beta2.fc26, tilix-1.6.1-1.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.