Use PRIVATE_CXX in HOST modules.

This fixes the build error:
out/host/linux-x86/obj/SHARED_LIBRARIES/libneo_util_intermediates/neo_err.o:
file not recognized: File format not recognized
See also CL #84578

Change-Id: Ib91230c7a5c9809eb1935959eaa9be8fa7c596b9
1 file changed