[MIR reviewer's template] Clarity around the `dh_makeshlibs -V` rule

[pushkarnk]

I recently reviewed gpgmepp which has C++ bindings for GPGME. The package ships a libgpgmepp7 library but has no .symbols file - the documented reason is that C++ symbol mangling is not consistent across architectures.

The MIR reviewer's template on line 303 states:

RULE: - If it's a library, does it either have a symbols file or use an empty
RULE:   argument to dh_makeshlibs -V? (pass such a patch on to Debian, but
RULE:   don't block on it).

This means in the absence of a symbols file, we expect d/rules to have:

override_dh_makeshlibs:
     dh_makeshlibs -V

However, it turns out that -V with empty argument has the same effect as completely omitting -V. Both lead to the use of -VUpstream-Version for debhelper-compat >= 12.

See the dh_makeshlibs snippet here:

		if ($v_flag_set) {
			if ($shlibs_file) {
                            ...
			} else {
				# Set the default "-V" (with no value) is passed.
				$v_flag = 'Upstream-Version' if $v_flag eq '';  ### empty -V
			}
		} elsif ($v_flag eq '') {
			# Set the default if "-V" is omitted.   
			$v_flag = compat(11) ? 'None' : 'Upstream-Version';  ### omitted -V
		}

It looks like if no override_dh_makeshlibs already exists, no change is necessary. Can we simplify the rule or add this clarification?