systemd: add libpcre2 as RRECOMMENDS if pcre2 is enabled

The libpcre2 is now dlopen'ed, so it is not automatically added to the
RDEPENDS anymore. Add it to the RRECOMMENDS list (and not RDEPENDS as
systemd tags the library as "suggested").

This issue is not on master, the systemd v257 recipe uses a tool that
systemd provides to get this kind of dependencies. But this cannot be
backported to scarthgap as systemd v255 does not have this tool yet.

Cc: Yoann Congal <yoann.congal@smile.fr>
(From OE-Core rev: 45fc7048c511c433ecc23840fe6fdd61f6366a47)

Signed-off-by: Alexis Cellier <alexis.cellier@smile.fr>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/recipes-core/systemd/systemd_255.17.bb

@@ -188,7 +188,7 @@ PACKAGECONFIG[oomd] = "-Doomd=true,-Doomd=false"
 PACKAGECONFIG[openssl] = "-Dopenssl=true,-Dopenssl=false,openssl"
 PACKAGECONFIG[p11kit] = "-Dp11kit=true,-Dp11kit=false,p11-kit"
 PACKAGECONFIG[pam] = "-Dpam=true,-Dpam=false,libpam,${PAM_PLUGINS}"
-PACKAGECONFIG[pcre2] = "-Dpcre2=true,-Dpcre2=false,libpcre2"
+PACKAGECONFIG[pcre2] = "-Dpcre2=true,-Dpcre2=false,libpcre2,,libpcre2"
 PACKAGECONFIG[polkit] = "-Dpolkit=true,-Dpolkit=false"
 # If polkit is disabled and networkd+hostnamed are in use, enabling this option and
 # using dbus-broker will allow networkd to be authorized to change the