security/kleopatra: Fix build against libc++18

libc++ 18 by default removes unique() in 'std::shared_ptr' (in <memory>), as
a follow-up to this resolution:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0521r0.html

An alternative would be to get it back by defining
_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE before including the libc++
headers, but trying to fight the standard may not be a wise move going forward,
especially if/as other C++ libraries follow suit.

Upstream MR (approved) is at
https://invent.kde.org/pim/kleopatra/-/merge_requests/205.

PR:             279139
Approved by:    kde (maintainer)
Approved by:    jrm (ports)
Approved by:    markj (mentor)

security/kleopatra/files/patch-src_crypto_recipient.cpp

@@ -0,0 +1,14 @@
+Submitted upstream: https://invent.kde.org/pim/kleopatra/-/merge_requests/205.
+To remove when updating to next release.
+
+--- src/crypto/recipient.cpp.orig	2024-02-11 04:00:57 UTC
++++ src/crypto/recipient.cpp
+@@ -85,7 +85,7 @@ void Recipient::detach()
+ 
+ void Recipient::detach()
+ {
+-    if (d && !d.unique()) {
++    if (d && d.use_count() != 1) {
+         d.reset(new Private(*d));
+     }
+ }

security/kleopatra/files/patch-src_crypto_sender.cpp

@@ -0,0 +1,14 @@
+Submitted upstream: https://invent.kde.org/pim/kleopatra/-/merge_requests/205.
+To remove when updating to next release.
+
+--- src/crypto/sender.cpp.orig	2024-02-11 04:00:57 UTC
++++ src/crypto/sender.cpp
+@@ -91,7 +91,7 @@ void Sender::detach()
+ 
+ void Sender::detach()
+ {
+-    if (d && !d.unique()) {
++    if (d && d.use_count() != 1) {
+         d.reset(new Private(*d));
+     }
+ }