* tests/scripts/features/patternrules: Check unreadable file support

tests/scripts/features/patternrules

diff --git a/tests/scripts/features/patternrules b/tests/scripts/features/patternrules
index 158a3ff..716cf4e 100644
--- a/tests/scripts/features/patternrules
+++ b/tests/scripts/features/patternrules
@@ -673,25 +673,27 @@
 }
 
 # SV 66268. An error message about a failure to remove an intermediate file.
-run_make_test(q!
-all: hello.x
-%.x: b/%.q; $(info $@ from $<)
-b/%.q:; @mkdir b; touch $@; chmod -w b
-!, '', "hello.x from b/hello.q\nrm b/hello.q\n#MAKE#: unlink: b/hello.q: $ERR_unreadable_file\n");
+if (defined $ERR_unreadable_file) {
+  run_make_test(q!
+  all: hello.x
+  %.x: b/%.q; $(info $@ from $<)
+  b/%.q:; @mkdir b; touch $@; chmod -w b
+  !, '', "hello.x from b/hello.q\nrm b/hello.q\n#MAKE#: unlink: b/hello.q: $ERR_unreadable_file\n");
 
-chmod(0754, 'b');
-unlink('b/hello.q');
-rmdir('b');
+  chmod(0754, 'b');
+  unlink('b/hello.q');
+  rmdir('b');
 
-run_make_test(q!
-all: hello.x
-%.x: b/%.q; $(info $@ from $<)
-b/%.q:; @mkdir b; touch $@; chmod -w b
-!, '-s', "hello.x from b/hello.q\n#MAKE#: unlink: b/hello.q: $ERR_unreadable_file\n");
+  run_make_test(q!
+  all: hello.x
+  %.x: b/%.q; $(info $@ from $<)
+  b/%.q:; @mkdir b; touch $@; chmod -w b
+  !, '-s', "hello.x from b/hello.q\n#MAKE#: unlink: b/hello.q: $ERR_unreadable_file\n");
 
-chmod(0754, 'b');
-unlink('b/hello.q');
-rmdir('b');
+  chmod(0754, 'b');
+  unlink('b/hello.q');
+  rmdir('b');
+}
 
 # SV 66273. An explicitly mentioned prerequisite is not intermediate, even in
 # the case of double colon.