meson.build: allow systemd service installation without systemd at buildtime

If the unit directory is already provided, we don't need systemd.

It allows Alpine to package systemd services (e.g. for postmarketOS) without
having systemd in Alpine.

Signed-off-by: Achill Gilgenast <[email protected]>

Author: fossdd

meson.build

@@ -13,9 +13,10 @@ prefix = get_option('prefix')
 with_qrtr_ns = get_option('qrtr-ns')
 
 install_systemd_unit = get_option('systemd-service')
-systemd = dependency('systemd', required : install_systemd_unit)
-if systemd.found()
-        systemd_system_unit_dir = get_option('systemd-unit-prefix')
+systemd_system_unit_dir = get_option('systemd-unit-prefix')
+systemd = dependency('systemd', required : false)
+enable_systemd = systemd.found() or (install_systemd_unit and systemd_system_unit_dir != '')
+if enable_systemd
         if systemd_system_unit_dir == ''
                 systemd_system_unit_dir = systemd.get_variable(
                         pkgconfig : 'systemdsystemunitdir',
@@ -31,7 +32,7 @@ subdir('lib')
 subdir('include')
 subdir('src')
 
-if systemd.found() and with_qrtr_ns.enabled()
+if enable_systemd and with_qrtr_ns.enabled()
         systemd_unit_conf = configuration_data()
         systemd_unit_conf.set('prefix', prefix)
         configure_file(