move "illegal anon sub" error from toke.c to perly.y

This fixes the TODO test in t/op/anonsub.t, but breaks two other tests:

- t/op/anonsub.t

        not ok 12 - '{ $x = sub }' is illegal
        # Failed test 12 - '{ $x = sub }' is illegal at t/op/anonsub.t line 15
        #      got 'Global symbol \"$x\" requires explicit package name (did you forget to declare \"my $x\"?) at (eval 12) line 1, <DATA> line 87.\nIllegal declaration of anonymous subroutine at (eval 12) line 1, at EOF\n'
        # expected /(?^:^Illegal declaration of anonymous subroutine at)/

- t/lib/croak.t

        FILE: lib/croak/toke ; line 644
        PROG:
        no feature 'apostrophe_as_package_separator';
        sub 'Hello'_he_said (_);
        EXPECTED:
        Illegal declaration of anonymous subroutine at - line 2.
        EXIT STATUS: != 0
        GOT:
        Bareword found where operator expected (Missing operator before "_he_said"?) at - line 2, near "'Hello'_he_said"
        Illegal declaration of anonymous subroutine at - line 2, near "sub 'Hello'"
        Execution of - aborted due to compilation errors.
        EXIT STATUS: 255
        not ok 247 - tick in names: initial character of sub name (no feature)
        # Failed test 247 - tick in names: initial character of sub name (no feature) at lib/croak/toke line 644

Since we don't immediately error out from the lexer anymore, the parser
may accumulate more errors before failing with "Illegal declaration of
anonymous subroutine".

See #5959.

Author: mauke