closes bpo-34652: Always disable lchmod on Linux. (GH-9234)

Misc/NEWS.d/next/Library/2018-09-12-14-46-51.bpo-34652.Rt1m1b.rst

+Ensure :func:`os.lchmod` is never defined on Linux.

configure

@@ -11285,6 +11285,17 @@ fi
 done
 
 
+# Force lchmod off for Linux. Linux disallows changing the mode of symbolic
+# links. Some libc implementations have a stub lchmod implementation that always
+# returns an error.
+if test "$MACHDEP" != linux; then
+  ac_fn_c_check_func "$LINENO" "lchmod" "ac_cv_func_lchmod"
+if test "x$ac_cv_func_lchmod" = xyes; then :
+
+fi
+
+fi
+
 ac_fn_c_check_decl "$LINENO" "dirfd" "ac_cv_have_decl_dirfd" "#include <sys/types.h>
        #include <dirent.h>
 "

configure.ac

@@ -3454,6 +3454,13 @@ AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  truncate uname unlinkat unsetenv utimensat utimes waitid waitpid wait3 wait4 \
  wcscoll wcsftime wcsxfrm wmemcmp writev _getpty)
 
+# Force lchmod off for Linux. Linux disallows changing the mode of symbolic
+# links. Some libc implementations have a stub lchmod implementation that always
+# returns an error.
+if test "$MACHDEP" != linux; then
+  AC_CHECK_FUNC(lchmod)
+fi
+
 AC_CHECK_DECL(dirfd,
     AC_DEFINE(HAVE_DIRFD, 1,
               Define if you have the 'dirfd' function or macro.), ,