[LLDB] Ensure LLDB symbols are exported in LLDB_EXPORT_ALL_SYMBOLS is provided.

[LLDB] Ensure LLDB symbols are exported in LLDB_EXPORT_ALL_SYMBOLS is provided.

If we want to export all lldb symbols (i.e LLDB_EXPORT_ALL_SYMBOLS=ON), we need to use default visibility for all LLDB libraries even if a global CMAKE_CXX_VISIBILITY_PRESET=hidden is present. In fact, there are cases in which a global llvm configuration wants CMAKE_CXX_VISIBILITY_PRESET as hidden but simultaneously LLDB_EXPORT_ALL_SYMBOLS=ON is also needed to be able to develop out-of-tree lldb plugins.

Differential Revision: https://reviews.llvm.org/D147453