Emit cxx interop into DW_AT_APPLE_flags
When compiling with interop enabled, emit the C++ interop compiler flag
into the DW_AT_APPLE_flags, to make it so LLDB can accurately match the
C++ interop mode when initializing its compiler instance.
rdar://97610458
(cherry picked from commit b1dbb0a3214882269c968bf0f9794570a4b2e7d7)
