Fix a crash-on-valid where a block capture copy expression was
picking up cleanups from earlier in the statement.  Also fix a
crash-on-invalid where a reference to an invalid decl from an
enclosing scope was causing an expression to fail to build, but
only *after* a cleanup was registered from that statement,
causing an assertion downstream.

The crash-on-valid is rdar://13459289.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177692 91177308-0d34-0410-b5e6-96231b3b80d8