Handle AT_SYMLINK_NOFOLLOW in __syscall_faccessat

The assertion in __syscall_faccessat only allowed AT_EACCESS, causing
a crash when AT_SYMLINK_NOFOLLOW was passed (e.g. by GLib's
g_local_file_query_exists which uses AT_EACCESS | AT_SYMLINK_NOFOLLOW).

Accept AT_SYMLINK_NOFOLLOW and use it to control whether symlinks are
followed during the path lookup.

Author: thiblahute

src/lib/libsyscall.js

@@ -930,14 +930,15 @@ var SyscallsLibrary = {
   __syscall_faccessat: (dirfd, path, amode, flags) => {
     path = SYSCALLS.getStr(path);
 #if ASSERTIONS
-    assert(!flags || flags == {{{ cDefs.AT_EACCESS }}});
+    assert(!flags || !(flags & ~({{{ cDefs.AT_EACCESS }}} | {{{ cDefs.AT_SYMLINK_NOFOLLOW }}})));
 #endif
     path = SYSCALLS.calculateAt(dirfd, path);
     if (amode & ~{{{ cDefs.S_IRWXO }}}) {
       // need a valid mode
       return -{{{ cDefs.EINVAL }}};
     }
-    var lookup = FS.lookupPath(path, { follow: true });
+    var nofollow = !!(flags & {{{ cDefs.AT_SYMLINK_NOFOLLOW }}});
+    var lookup = FS.lookupPath(path, { follow: !nofollow });
     var node = lookup.node;
     if (!node) {
       return -{{{ cDefs.ENOENT }}};