[Bug c/95011] Error building gcc 10.1.0 on macOS Catalina with Xcode 11.4.1

[mario_grgic at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95011

--- Comment #1 from mario_grgic at hotmail dot com ---
It looks like this is configuration error. --with-sysroot and
--with-native-system-header-dir must both be specified when building on macOS.
However, configure --help does not list or document either of them.