app-misc/mosquitto has an optional 'websockets' USE-flag. this dependency pulls in net-libs/libwebsockets. unless libwebsockets is built with the 'lejp' USE-flag, building mosquitto with 'websockets' will fail. net-libs/libwebsockets-3.2.0 app-misc/mosquitto-1.6.7
In addition to fixing the dependency in mosquitto, libwebsockets' lejp USE flag should probably be enabled by default since it adds no dependencies.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=7c16ad6e181ac72bc15ad81ff394e8d52858ba04 commit 7c16ad6e181ac72bc15ad81ff394e8d52858ba04 Author: Matt Turner <mattst88@gentoo.org> AuthorDate: 2019-12-20 20:40:59 +0000 Commit: Matt Turner <mattst88@gentoo.org> CommitDate: 2019-12-20 21:58:53 +0000 app-misc/mosquitto: Version bump to 1.6.8 Closes: https://bugs.gentoo.org/696946 Closes: https://bugs.gentoo.org/700816 Signed-off-by: Matt Turner <mattst88@gentoo.org> app-misc/mosquitto/Manifest | 1 + app-misc/mosquitto/mosquitto-1.6.8.ebuild | 114 ++++++++++++++++++++++++++++++ 2 files changed, 115 insertions(+) https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=ba93d0691dc516c51fbe99d9977e7555810f20fd commit ba93d0691dc516c51fbe99d9977e7555810f20fd Author: Matt Turner <mattst88@gentoo.org> AuthorDate: 2019-12-20 20:23:00 +0000 Commit: Matt Turner <mattst88@gentoo.org> CommitDate: 2019-12-20 21:58:44 +0000 net-libs/libwebsockets: Version bump to 3.2.1 - enable IUSE=lejp by default (bug #700816) - Change subslot to match libwebsockets soname Closes: https://bugs.gentoo.org/700816 Signed-off-by: Matt Turner <mattst88@gentoo.org> net-libs/libwebsockets/Manifest | 1 + net-libs/libwebsockets/libwebsockets-3.2.1.ebuild | 77 +++++++++++++++++++++++ 2 files changed, 78 insertions(+)