In build_supporting_libs.py, print output from build commands only if they fail
In build_supporting_libs.py, print output from build commands only if they fail

In addition to greatly reducing the length of the build log, this prevents Xcode from mistaking ignorable error messages for actual failures.

mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks,mworks/mworks