Fix LLDB search order

Fix LLDB search order

By default 'find_library' without 'NO_DEFAULT_PATH' keyword searches
first in default locations specified by '${CMAKE_SYSTEM_PREFIX_PATH}'
and only then in locations specified via 'PATHS' keyword
('${WITH_LLDB_LIBS}' in our case). As result it always picks-up default
LLDB ignoring the one explicitly specified via '${WITH_LLDB_LIBS}'.
This change modifies search order giving priority to '${WITH_LLDB_LIBS}'
and '${WITH_LLDB_INCLUDES}' over default locations.

Commit migrated from https://github.com/dotnet/coreclr/commit/c1b65bdc225386e4f2af4c49512fbb93579c0973