The build system of openinventor calls gcc as /usr/bin/gcc, effectively disabling distcc compilation (which works by prefixing /usr/lib/distcc/bin to the normal PATH). While this is not a fatal bug, it makes all compiles native which in turn drags out compilation for those who have slow machines and hence use distcc. Especially so since it's compiling mostly C++ which is rather slow anyway.
fixed in cvs, thanks for the report.
