[lldb][modules] Disable Clang Modules in source/Host directory on macOS

Summary:
The arpa/inet.h header in macOS is providing an incorrect htonl
function with enabled local submodule visibility while building LLDB. This
caused several networking tests to fail as the IP addresses are now flipped
in LLDB.

This patch disables building with modules when local submodule visibility is
active and the current system is macOS for the source/Host directory (which
is the *only directory that includes arpa/inet.h).

* debugserver also includes arpa/inet.h but there we already disabled
modules.

Reviewers: aprantl

Reviewed By: aprantl

Subscribers: mgorny, JDevlieghere

Differential Revision: https://reviews.llvm.org/D79632