libsystemd: install sd-path.h and export sd_path_lookup{,_strv}

Those are not terribly imporant functions, but we have them, and there's
no reason not to export them.

src/libsystemd/libsystemd.sym

@@ -697,3 +697,9 @@ global:
         sd_event_source_send_child_signal;
         sd_journal_open_namespace;
 } LIBSYSTEMD_243;
+
+LIBSYSTEMD_246 {
+global:
+        sd_path_lookup;
+        sd_path_lookup_strv;
+} LIBSYSTEMD_245;

src/systemd/meson.build

@@ -12,6 +12,7 @@ _systemd_headers = '''
         sd-journal.h
         sd-login.h
         sd-messages.h
+        sd-path.h
 '''.split()
 
 # https://github.com/mesonbuild/meson/issues/1633
@@ -30,7 +31,6 @@ _not_installed_headers = '''
         sd-ndisc.h
         sd-netlink.h
         sd-network.h
-        sd-path.h
         sd-radv.h
         sd-resolve.h
         sd-utf8.h