This patch adds functionality and a test for importing Objective-C classes
and their methods.

It also adds a flag to clang-import-test to set the language used for
parsing. This takes the same argument format as the -x option to the
driver.

Differential Revision: https://reviews.llvm.org/D35274


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@309014 91177308-0d34-0410-b5e6-96231b3b80d8