See this document for details: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/changes.rst These are normally installed on most systems as gcc build deps, but wouldn't be on systems using binary packages.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=458979ce33f4482d4f4ee7e7bc4bfdd301feef58 commit 458979ce33f4482d4f4ee7e7bc4bfdd301feef58 Author: Thomas Deutschmann <whissi@gentoo.org> AuthorDate: 2018-08-09 00:21:11 +0000 Commit: Thomas Deutschmann <whissi@gentoo.org> CommitDate: 2018-08-09 00:32:28 +0000 kernel-2.eclass: add sys-devel/bison and sys-devel/flex to RDEPEND Since commit 033dba2ec06 [Link 1], kernel needs bison and flex. Link 1: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=033dba2ec06c47a9fe1b190bc3281058fb20738d Closes: https://bugs.gentoo.org/663020 eclass/kernel-2.eclass | 2 ++ 1 file changed, 2 insertions(+)