Add bitreader to LINK_COMPONENTS in users of libclang, c-arcmt-test and c-index-test.

They don't link cygclang.dll, but libclang.a on cygwin.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172980 91177308-0d34-0410-b5e6-96231b3b80d8