[CodeGen] Make sure the EH cleanup for block captures is conditional when the block...

[CodeGen] Make sure the EH cleanup for block captures is conditional when the block literal is in a conditional context

Previously, clang was crashing on the attached test because the EH cleanup for
the block capture was incorrectly emitted under the assumption that the
expression wasn't conditionally evaluated. This was because before 9a52de00260,
pushLifetimeExtendedDestroy was mainly used with C++ automatic lifetime
extension, where a conditionally evaluated expression wasn't possible. Now that
we're using this path for block captures, we need to handle this case.

rdar://66250047

Differential revision: https://reviews.llvm.org/D86854