Hi, I haven't had an in-depth look yet, but I know a work-around:
run 
emerge -i --target=gitHEAD cmake-pkg
and then go ahead.
This will hopefully be fixed in the next cmake release.

If 3.4.1 is known to be broken, and the last version (3.3.1) used to work fine, then please just downgrade in cmake.py @ Patrick.

@Reporter: Can you confirm upgrading to master / downgrading to 3.3.1 fixes the issue for you?

Created attachment 96910 [details]
attachment-12937-0.html

I've got those too, is there any known solution?

2015-12-28 1:39 GMT-02:00 Shunsuke Shimizu via KDE Bugzilla <
bugzilla_noreply@kde.org>:

> https://bugs.kde.org/show_bug.cgi?id=357240
>
>             Bug ID: 357240
>            Summary: emerging KCoreAddons fails by CMake Internal Error on
>                     Win 8.1 x64
>            Product: kde-windows
>            Version: unspecified
>           Platform: MS Windows
>                 OS: MS Windows
>             Status: UNCONFIRMED
>           Severity: normal
>           Priority: NOR
>          Component: buildsystem
>           Assignee: kde-windows@kde.org
>           Reporter: grafi@grafi.jp
>
> I'm using Windows 8.1 x64.
> I checkout the master of emerge, and make the build target x64 by editing
> kdesettings.ini (other parts are kept unchanged).
> I tried on two machines and the result was same.
>
> Reproducible: Always
>
> Steps to Reproduce:
> 1. checkout the master branch of emerge
> 2. make the target x64
> 3. emerge kcoreaddons (I encountered to the error when emerging
> frameworks,
> after qt is emerged)
>
>
> Actual Results:
> PS R:\> emerge kcoreaddons
> emerge debug: buildAction: all
> emerge debug: packageName: ['kcoreaddons']
> emerge debug: buildType: RelWithDebInfo
> emerge debug: buildTests: False
>
> ________________________________________________________________________________
> emerge debug: fetching [git]kde:kcoreaddons|master|
> Already up-to-date.
> Already on 'master'
> Your branch is up-to-date with 'origin/master'.
> Already up-to-date.
> Already on 'master'
> Your branch is up-to-date with 'origin/master'.
> entering:
> r:\build\frameworks\kcoreaddons\work\mingw-w64-RelWithDebInfo-master
> cleaning
> r:\build\frameworks\kcoreaddons\work\mingw-w64-RelWithDebInfo-master
> entering:
> r:\build\frameworks\kcoreaddons\work\mingw-w64-RelWithDebInfo-master
> emerge debug: cmake -G "MinGW Makefiles"  -DCMAKE_INSTALL_PREFIX="r:/"
> -DCMAKE_PREFIX_PATH="r:/" -DCMAKE_BUILD_TYPE=RelW
> ithDebInfo "q:\kcoreaddons"
> -- The C compiler identification is GNU 5.2.0
> -- The CXX compiler identification is GNU 5.2.0
> -- Check for working C compiler: R:/mingw64/bin/gcc.exe
> -- Check for working C compiler: R:/mingw64/bin/gcc.exe -- works
> -- Detecting C compiler ABI info
> -- Detecting C compiler ABI info - done
> -- Detecting C compile features
> -- Detecting C compile features - done
> -- Check for working CXX compiler: R:/mingw64/bin/g++.exe
> -- Check for working CXX compiler: R:/mingw64/bin/g++.exe -- works
> -- Detecting CXX compiler ABI info
> -- Detecting CXX compiler ABI info - done
> -- Detecting CXX compile features
> -- Detecting CXX compile features - done
> --
>
> -- Looking for __GLIBC__
> -- Looking for __GLIBC__ - not found
> -- Could NOT find FAM (missing:  FAM_INCLUDE_DIR FAM_LIBRARIES)
> -- Looking for include file sys/inotify.h
> -- Looking for include file sys/inotify.h - not found
> -- Looking for include files sys/types.h, sys/mman.h
> -- Looking for include files sys/types.h, sys/mman.h - not found
> -- Looking for getgrouplist
> -- Looking for getgrouplist - not found
> -- Performing Test COMPILER_HAS_DEPRECATED_ATTR
> -- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success
> -- Found SharedMimeInfo: R:/bin/update-mime-database.exe (found suitable
> version "0.71", minimum required is "0.70")
> -- Performing Test HAVE_QFILESYSTEMWATCHER
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> CMake Internal Error (please report a bug):
>   Missing cmGeneratorTarget instance!
>
> Note: The stack could not be examined because backtrace is not supported.
>
>
> -- Performing Test HAVE_QFILESYSTEMWATCHER - Success
> --
> -- The following OPTIONAL packages have been found:
>
>  * SharedMimeInfo (required version >= 0.70) , A database of common MIME
> types
> , <http://freedesktop.org/wiki/Software/s
> hared-mime-info/>
>    Allows KDE applications to determine file types
>
> -- The following REQUIRED packages have been found:
>
>  * ECM (required version >= 5.17.0) , Extra CMake Modules. ,
> <https://projects.kde.org/projects/kdesupport/extra-cmake-m
> odules>
>  * Qt5Core
>  * Qt5 (required version >= 5.3.0)
>
> -- The following OPTIONAL packages have not been found:
>
>  * FAM , File alteration notification support via a separate service ,
> <http://oss.sgi.com/projects/fam>
>    Provides file alteration notification facilities using a separate
> service.
> FAM provides additional support for NFS.
>
> -- Configuring incomplete, errors occurred!
> See also
>
> "R:/build/frameworks/kcoreaddons/work/mingw-w64-RelWithDebInfo-master/CMakeFiles/CMakeOutput.log".
> See also
>
> "R:/build/frameworks/kcoreaddons/work/mingw-w64-RelWithDebInfo-master/CMakeFiles/CMakeError.log".
> emerge warning: while running configure cmd: cmake -G "MinGW Makefiles"
> -DCMAKE_INSTALL_PREFIX="r:/" -DCMAKE_PREFIX_PAT
> H="r:/" -DCMAKE_BUILD_TYPE=RelWithDebInfo "q:\kcoreaddons"
> emerge error: fatal error: package frameworks/kcoreaddons all failed
>
> --
> You are receiving this mail because:
> You are the assignee for the bug.
> _______________________________________________
> Kde-windows mailing list
> Kde-windows@kde.org
> https://mail.kde.org/mailman/listinfo/kde-windows
>

(In reply to Kevin Funk from comment #2)
> If 3.4.1 is known to be broken, and the last version (3.3.1) used to work
> fine, then please just downgrade in cmake.py @ Patrick.
> 
> @Reporter: Can you confirm upgrading to master / downgrading to 3.3.1 fixes
> the issue for you?

Sorry for the late reply.
 emerge -i --target=gitHEAD cmake
helped for me.

Now cmake 3.4.3 (and 3.4.2) have been released.
So updating cmake's ebuild should fix the problem.

I made the nightly the default target for now as 3.4.3 is still broken.

Thank you for the bug report.

As this report hasn't seen any changes in 5 years or more, we ask if you can please confirm that the issue still persists.

If this bug is no longer persisting or relevant please change the status to resolved.