[OPENMP] Support for mapping of the lambdas in target regions.

[OPENMP] Support for mapping of the lambdas in target regions.

Added support for mapping of lambdas in the target regions. It scans all
the captures by reference in the lambda, implicitly maps those variables
in the target region and then later reinstate the addresses of
references in lambda to the correct addresses of the captured|privatized
variables.

llvm-svn: 345609