various: check meson feature flag early

Prompted by https://github.com/systemd/systemd/pull/35110#discussion_r1835885340

src/cryptsetup/meson.build

@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
+if conf.get('HAVE_LIBCRYPTSETUP') != 1
+        subdir_done()
+endif
+
 subdir('cryptsetup-tokens')
 
 systemd_cryptsetup_sources = files(
@@ -15,7 +19,6 @@ executables += [
         executable_template + {
                 'name' : 'systemd-cryptsetup',
                 'public' : true,
-                'conditions' : ['HAVE_LIBCRYPTSETUP'],
                 'sources' : systemd_cryptsetup_sources,
                 'dependencies' : [
                         libcryptsetup,
@@ -25,14 +28,11 @@ executables += [
         },
         generator_template + {
                 'name' : 'systemd-cryptsetup-generator',
-                'conditions' : ['HAVE_LIBCRYPTSETUP'],
                 'sources' : files('cryptsetup-generator.c'),
         },
 ]
 
-if conf.get('HAVE_LIBCRYPTSETUP') == 1
-        # symlink for backwards compatibility after rename
-        meson.add_install_script(sh, '-c',
-                                 ln_s.format(bindir / 'systemd-cryptsetup',
-                                             libexecdir / 'systemd-cryptsetup'))
-endif
+# symlink for backwards compatibility after rename
+meson.add_install_script(sh, '-c',
+                         ln_s.format(bindir / 'systemd-cryptsetup',
+                                     libexecdir / 'systemd-cryptsetup'))