Gentoo's Bugzilla –
Attachment 586722 Details for
Bug 692078dev-qt/qtwayland-5.12.4-r1 with dev-qt/qtgui built with LTO - lto1: fatal error: bytecode stream in file ‘/usr/lib64/libQt5FontDatabaseSupport.a’ generated with LTO version 8.0 instead of the expected 8.1