If a command fails, make sure the target is deleted.  This came up with failure
to build dragonegg-lit.site.cfg due to sed barfing after creating an empty file
for the target.  Running again would then do the wrong thing as make would think
that target had been made already, due to the empty file.


git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@175612 91177308-0d34-0410-b5e6-96231b3b80d8