More details can be found in log files
Created attachment 182867 [details] kdelibs-4.2.0-r2 build log (stopped at 50%)
Created attachment 182868 [details] Related environment info
The problem seems to be related to QtSvg. Probably you should re-install qt-svg (and probably also qt-gui). What version (overlay?) of qt4 do you use?
Yes , rebuilding qt-svg should solve your issue
Mixing different versions of qt-* packages (for example qt-core-4.5 with qt-svg-4.4) is unsupported and this causes this issue.
Oh, and as a solution - emerge -vaDu world