Fix the type of the capture passed to LambdaIntroducer::addCapture in

RebuildLambdaScopeInfo

Previously the type of the variable was being passed, which was causing
clang to crash when a non-reference variable was captured by reference
or a reference variable was captured by value by a lambda and a block
nested inside the lambda body was referencing the variable.

Original patch by JF Bastien.

rdar://problem/47550338

Differential Revision: https://reviews.llvm.org/D58164