Created attachment 434844 [details] emerge --info Hello. $SUBJECT Please fix.
Created attachment 434846 [details] emerge -pqv wlc
Created attachment 434848 [details] build.log
Created attachment 434850 [details] CMakeOutput.log
Created attachment 434852 [details] CMakeError.log
From looking at the build.log, I notice that you are probably not using the updated live ebuild, and that is causing the issue. Upstream changed how X11 support is configured (introduced a new CMake option), and configure fails if we attempt to configure it the old way. Yesterday, I updated the live ebuild for these changes, and sent a github pull request. It got merged today, some hours ago. I don't know what the delay is until updates actually become available in official mirrors for users to sync. You should try using this new ebuild. There should be no X11 configuration issues with it.
Indeed, after updating my local tree the problem is gone. Thank you. Fixed in: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=db4d55839812cc09f9eeded3939012d69a5cb161