Fix computation of linkage within nested lambdas.
 When nested lambdas are used in NSDMI's - this prevents infinite recursion.

See http://llvm-reviews.chandlerc.com/D1783 for Doug's approval regarding the code, and then request for some tests.

[On a related note, I need this patch so as to pass tests of transformations of nested lambdas returned from member functions]


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@191645 91177308-0d34-0410-b5e6-96231b3b80d8
Remove an unnecessary overload from ASTLambda.h 
As Richard pointed out to me, dyn_cast is very cheap - there is no real benefit from adding cluttery overloads to only avoid that cast.
No functionality change.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@191646 91177308-0d34-0410-b5e6-96231b3b80d8
Revert the linkage fix.
I got a bunch of buildbot failures that i don't understand - sorry.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@191647 91177308-0d34-0410-b5e6-96231b3b80d8