meson: add feature flag for nspawn build (#36876)

Other tools have it, nspawn doesn't, add one

test/fuzz/meson.build

@@ -60,7 +60,7 @@ sanitize_address_undefined = custom_target(
                    'fuzzers',
                    ' '.join(fuzz_c_args + '-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION'),
                    ' '.join(fuzz_cpp_args + '-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION'),
-                   '-Dfuzz-tests=true -Db_lundef=false -Db_sanitize=address,undefined --optimization=@0@ @1@ --auto-features=@2@'.format(
+                   '-Dfuzz-tests=true -Db_lundef=false -Db_sanitize=address,undefined -Dnspawn=enabled --optimization=@0@ @1@ --auto-features=@2@'.format(
                            get_option('optimization'),
                            get_option('werror') ? '--werror' : '',
                            sanitize_auto_features

test/meson.build

@@ -359,11 +359,9 @@ if install_tests
                                exclude_files : '.gitattributes',
                                install_dir : testdata_dir)
         endif
-        if conf.get('ENABLE_RESOLVE') == 1
-                install_subdir('test-resolve',
-                               exclude_files : '.gitattributes',
-                               install_dir : testdata_dir)
-        endif
+        install_subdir('test-resolve',
+                       exclude_files : '.gitattributes',
+                       install_dir : testdata_dir)
 
         # The unit tests implemented as shell scripts expect to find testdata/
         # in the directory where they are stored.

test/units/TEST-13-NSPAWN.sh

@@ -10,6 +10,11 @@ if [[ "$FSTYPE" == "fuseblk" ]]; then
     exit 77
 fi
 
+if ! command -v systemd-nspawn >/dev/null; then
+    echo "no systemd-nspawn" >/skipped
+    exit 77
+fi
+
 # shellcheck source=test/units/test-control.sh
 . "$(dirname "$0")"/test-control.sh