hwdb-test: pass an explit path to systemd-hwdb

https://github.com/systemd/systemd/pull/19316 failed with:
[1065/1670] Linking target systemd-hwdb
--- command ---
14:28:29 /root/src/test/hwdb-test.sh
--- stdout ---
./systemd-hwdb does not exist, please build first

I'm not sure what is going on here… In principle meson says that tests may be
called from any directory, but in practice is was always the build directory.
So far we were relying on systemd-hwdb being present in '.', and this worked.
Either way, it's nicer to pass the exact path, so let's do that.

meson.build

@@ -3168,7 +3168,7 @@ if conf.get('ENABLE_TMPFILES') == 1
 endif
 
 if conf.get('ENABLE_HWDB') == 1
-        public_programs += executable(
+        systemd_hwdb = executable(
                 'systemd-hwdb',
                 'src/hwdb/hwdb.c',
                 include_directories : includes,
@@ -3176,6 +3176,14 @@ if conf.get('ENABLE_HWDB') == 1
                 install_rpath : udev_rpath,
                 install : true,
                 install_dir : rootbindir)
+        public_programs += systemd_hwdb
+
+        if want_tests != 'false'
+                test('hwdb-test',
+                     hwdb_test_sh,
+                     args : [systemd_hwdb.full_path()],
+                     timeout : 90)
+        endif
 endif
 
 if conf.get('ENABLE_QUOTACHECK') == 1

test/hwdb-test.sh

@@ -11,10 +11,10 @@ set -e
 
 export SYSTEMD_LOG_LEVEL=info
 ROOTDIR=$(dirname $(dirname $(readlink -f $0)))
-SYSTEMD_HWDB=./systemd-hwdb
+SYSTEMD_HWDB="${1:?missing argument}"
 
 if [ ! -x "$SYSTEMD_HWDB" ]; then
-    echo "$SYSTEMD_HWDB does not exist, please build first"
+    echo "$SYSTEMD_HWDB is not executable" >&2
     exit 1
 fi
 

test/meson.build

@@ -57,10 +57,8 @@ if install_tests
 endif
 
 test_network_generator_conversion_sh = find_program('test-network-generator-conversion.sh')
-
-############################################################
-
 test_systemd_tmpfiles_py = find_program('test-systemd-tmpfiles.py')
+hwdb_test_sh = find_program('hwdb-test.sh')
 
 ############################################################
 
@@ -128,17 +126,6 @@ endif
 
 ############################################################
 
-if conf.get('ENABLE_HWDB') == 1
-        hwdb_test_sh = find_program('hwdb-test.sh')
-        if want_tests != 'false'
-                test('hwdb-test',
-                     hwdb_test_sh,
-                     timeout : 90)
-        endif
-endif
-
-############################################################
-
 if want_tests != 'false' and dmi_arches.contains(host_machine.cpu_family())
         udev_dmi_memory_id_test = find_program('udev-dmi-memory-id-test.sh')