Updated the IRExecutionUnit to keep local copies

of the data it writes down into the process even
if the process doesn't exist.  This will allow
the IR interpreter to access static data allocated
on the expression's behalf.

Also cleaned up object ownership in the
IRExecutionUnit so that allocations are created
into the allocations vector.  This avoids needless
data copies.

<rdar://problem/13424594>

llvm-svn: 177456