This also avoids a fork bomb from the llvm-top/build script which
doesn't know how to handle cycles in the dependence graph.

llvm-svn: 39933

of the cyclic depndency between llvm and llvm-gcc-4-0.

llvm-svn: 39910

llvm-svn: 38521

of llvm from that level.

llvm-svn: 38423

llvm-svn: 38422