[clang] Fix linkage of nested lambdas.
patch from Philippe Daouadi <firstname.lastname@example.org>
This is an attempt to fix
This effectively reverts D1783. It
doesn't break the current tests and fixes the test that this commit
We now decide of a lambda linkage only depending on the visibility of
its parent context.
Differential Revision: https://reviews.llvm.org/D73701