gmu: pull pending upstream inclusion fix for ncurses-6.3
gmu: pull pending upstream inclusion fix for ncurses-6.3

Without the fix build on ncurses-6.3 fails as:

    src/tools/ui.c: In function 'ui_draw_footer_button':
    src/tools/ui.c:329:9: error: format not a string literal and no format arguments [-Werror=format-security]
      329 |         wprintw(ui->win_footer->win, key);
          |         ^~~~~~~

While at it pulled fix for upstream gcc-10 and clang-12 which
default to -fno-common. Otherwise build would fail as:

    $ nix build --impure --expr 'with import ./. {}; gmu.override { stdenv = clang12Stdenv; }' -L
    ...
    gmu> ld: feloader.o:(.bss+0x8): multiple definition of `dlsymunion';
      decloader.o:(.bss+0x8): first defined here

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