Fixed internal code to not link against and code from "lldb/API/*".

lldb_private::Debugger was #including some "lldb/API" header files which causes tools (lldb-platform and lldb-gdbserver) that link against the internals only (no API layer) to fail to link depending on which calls were being used.

Also fixed the current working directory so that it gets set correctly for remote test suite runs. Now the remote working directory is set to: "ARCH/TESTNUM/..." where ARCH is the current architecture name and "TESTNUM" is the current test number.

Fixed the "lldb-platform" and "lldb-gdbserver" to not warn about mismatched visibility settings by having each have their own exports file which contains nothing. This forces all symbols to not be exported, and also quiets the linker warnings.