Windows fix: Need to ensure all APIs are forward decl'd with LLDB_API. If not then frontend linker errors appear due to dllexport differences. There may be some others missing, will commit as I find them.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@206958 91177308-0d34-0410-b5e6-96231b3b80d8