GccVersionDeterminer should show better errors

When trying to determine the gcc version, the GccVersionDeterminer class captures stdout, but squelches stderr. If stdout gets no output, the build fails with the general error “Could not determine GCC version: failed to execute armv7l-meego-linux-gnueabi-gcc -dM -E -”. It would be helpful if stderr was actually captured and logged somewhere in this case, to make it easier to troubleshoot the underlying problem.

Of course, you can manually run the command given in order to see what the problem is - but it would be helpful to cut out this extra manual step.