[libc++][AIX] AIX allows for changing permissions of symlinks

The test fails on AIX due to it expecting an error as on Linux. However, as on
other non-Linux systems symlinks permissions are supported so expect an empty
error code.

Reviewed By: daltenty, #libc, ldionne

Differential Revision: https://reviews.llvm.org/D121140

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.permissions/permissions.pass.cpp

@@ -8,8 +8,6 @@
 
 // UNSUPPORTED: c++03
 
-// XFAIL: LIBCXX-AIX-FIXME
-
 // <filesystem>
 
 // void permissions(const path& p, perms prms,
@@ -164,7 +162,7 @@ TEST_CASE(test_no_resolve_symlink_on_symlink)
         {perms::owner_all, perms::group_all, perm_options::remove},
     };
     for (auto const& TC : cases) {
-#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__)
+#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(_AIX)
         // On OS X symlink permissions are supported. We should get an empty
         // error code and the expected permissions.
         const auto expected_link_perms = TC.expected;