My emerge ... @world failed with clang. I don't have the build log any more. I had 'MAKEOPTS="-j11"' in my make.conf. The error message said ninja -j11 (and one more or some more options) had an error. This error was not more specified or I didn't find it in the mixed messages of 11 threads. I changed to MAKEOPTS="-j1" emerged -1 clang, which took some time but was successfull and then changed my make.conf back and started emerge ... @world again. I have not investigated more. I guess some dependencies which are processed by ninja should be fixed. It works for me now, but was very time consuming and would have been much more time consuming if I would not got the lucky guess. If an ebuild cannot be build parallel there is a way to handle it within the ebuild. This would be a second solution if the ninja stuff cannot be fixed. Of cause it would be better if it would work parallel. I think I filed a similar bug with something some time ago. I don't remember which ebuild it was and couldn't find it here. THIS MIGHT BE A BUG IN NINJA OR IT'S DOCUMENTATION.
Can't help you without the details. It is entirely possible you've ran out of memory.
