build: Compile fuzz-journald-util.c only if want_fuzz_tests

fuzz-journald-util.c is compiled unconditionally even though fuzzing
tests aren't enabled. Only build it if fuzzing tests are configured.
This also ensure that the functions it uses from src/shared/tests.c are
available.

Fixes 32bd43d768
Closes #39984

Signed-off-by: Chris Hofer <christian.hofer@codasip.com>

src/journal/meson.build

@@ -19,11 +19,16 @@ systemd_journald_extract_sources = files(
         'journald-syslog.c',
         'journald-varlink.c',
         'journald-wall.c',
-        # Build fuzz-journald.c as part of systemd-journald so we only compile it once instead of once per
-        # fuzz test.
-        'fuzz-journald-util.c',
 )
 
+if want_fuzz_tests
+        # Build fuzz-journald-util.c as part of systemd-journald so we only
+        # compile it once instead of once per fuzz test.
+        systemd_journald_extract_sources += files(
+                'fuzz-journald-util.c',
+        )
+endif
+
 journald_gperf_c = custom_target(
         input : 'journald-gperf.gperf',
         output : 'journald-gperf.c',