With the upgrade of devel/qscintilla2 to 2.10 it now depends on std::regex, which is only available since c++11. This breaks builds with gcc, so "compiler:c++11-lib" needs to be added to the USES list (untested thus far, will verify once my current poudriere bulk build completes).
Verified, USES= compiler:c++11-lib makes it build.
A commit references this bug: Author: tcberner Date: Fri Mar 9 16:53:38 UTC 2018 New revision: 463975 URL: https://svnweb.freebsd.org/changeset/ports/463975 Log: Fix build of devel/qscintilla2 on gcc platforms. PR: 226452 Submitted by: jhibbits Changes: head/devel/qscintilla2/Makefile
Thanks for the fix!
Thanks for the report :)