Delete temporary output files when an error occurs during PCH reading.

Delete temporary output files when an error occurs during PCH reading.

This reduces the spam make test leaves behind in /tmp. The assert isn't
particularly useful because it's not run with -disable-free (the default when
using the clang driver) but should cover all -cc1 tests.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165910 91177308-0d34-0410-b5e6-96231b3b80d8