luks: make cryptsetup optional in test suite

The LUKS test directory is included unconditionally by the parent
meson.build (only gated by cross-compilation), but all LUKS tests
require the cryptsetup binary. When cryptsetup is unavailable (e.g.,
on macOS/Darwin or minimal build environments), the build fails at
configure time.

Make cryptsetup optional and use subdir_done() to skip the entire
test directory when it is not found. This also avoids the
luksmeta_data.get('OLD_CRYPTSETUP') error that occurs when
libcryptsetup was not detected.

Move the jq find_program() call after the cryptsetup guard since
it is only used within LUKS tests.

Author: sini

src/luks/tests/meson.build

@@ -1,9 +1,14 @@
 # We use jq for comparing the pin config in the clevis luks list tests.
 jq = find_program('jq', required: false)
 
-# We use cryptsetup for testing LUKS2 binding and saving the token in a
-# given token slot.
-cryptsetup = find_program('cryptsetup', required: true)
+# All LUKS tests require cryptsetup. The test directory is included
+# unconditionally by the parent meson.build, so we must handle the case
+# where cryptsetup is not available (e.g., on macOS/Darwin).
+cryptsetup = find_program('cryptsetup', required: false)
+if not cryptsetup.found()
+  warning('Will not run LUKS tests due to missing cryptsetup')
+  subdir_done()
+endif
 
 # Use keyctl to check an existing token id can be created from
 # kernel keyring password
@@ -14,6 +19,9 @@ else
     warning('keyutils not installed, unable to test existing token id binding')
 endif
 
+# We use jq for comparing the pin config in the clevis luks list tests.
+jq = find_program('jq', required: false)
+
 common_functions = configure_file(input: 'tests-common-functions.in',
   output: 'tests-common-functions',
   configuration: luksmeta_data,