The files in shared/nm-utils are not compiled as one static library,
instead each subproject that needs (parts of) them, re-compiles the
files individually.
The major reason for that is, because we might have different compile
flags, depending on whether we build libnm-core or
libnm-util/libnm-glib. Actually, I think that is not really the case,
and maybe this should be refactored, to indeed build them all as a
static library first.
Anyway, libnm-util, libnm-glib, clients' common lib, they all need a
different set of shared files that they should compile. Refactor
"shared/meson.build" to account for that and handle it like autotools
does.
Another change is, that "shared_c_siphash_dep" no longer advertises
"include_directories: include_directories('c-siphash/src')". We don't
put c-siphash.h into the include search path. Users who need it, should
include it via "#include <c-siphash/src/c-siphash.h>". The only exception
is when building shared_n_acd library, which is not under our control.