Fix cp permissions when copying symlink contents, and add test.

tests/cp.test

@@ -89,6 +89,13 @@ testing "-r dir1/* dir2" \
 	"cp -r one/* dir2 && diff -r one dir2 && echo yes" "yes\n" "" ""
 rm -rf one dir dir2
 
+touch walrus
+chmod 644 walrus
+ln -s walrus woot
+
+testing "symlink dest permissions" "cp woot carpenter && stat -c %A carpenter" \
+  "-rw-r--r--\n" "" ""
+
 # cp -r ../source destdir
 # cp -r one/two/three missing
 # cp -r one/two/three two

toys/posix/cp.c

@@ -268,6 +268,8 @@ static int cp_node(struct dirtree *try)
           catch = try->name;
           break;
         }
+        // When copying contents use symlink target's attributes
+        if (S_ISLNK(try->st.st_mode)) fstat(fdin, &try->st);
         fdout = openat(cfd, catch, O_RDWR|O_CREAT|O_TRUNC, try->st.st_mode);
         if (fdout >= 0) {
           xsendfile(fdin, fdout);