Two minor, related fixes for template instantiation with blocks:

  - Make sure that the block expression is instantiation-dependent if the
    block is in a dependent context
  - Make sure that the C++ 'this' expression gets captured even if we
  don't rebuild the AST node during template instantiation. This would
  also have manifested as a bug for lambdas.

Fixes <rdar://problem/10832617>.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151372 91177308-0d34-0410-b5e6-96231b3b80d8