Tell CMake about the SystemRuntime plugin.
This fixes CMake build on Darwin.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196575 91177308-0d34-0410-b5e6-96231b3b80d8
Typo in comments

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196577 91177308-0d34-0410-b5e6-96231b3b80d8