Fix maxLoopDepth computation in ScopInfo

The max loop depth was incorrectly computed for scops that contain a
block from a loop but do not contain the entire loop. We need to
check that the full loop is contained in the region when computing
the max loop depth.

These scops occur when a region containing an inner loop is expanded
to include some blocks from the outer loop, but it cannot be fully
expanded to contain the outer loop because the region containing the
outer loop is invalid.

Differential Revision: http://reviews.llvm.org/D6913

llvm-svn: 225812