Fix multi-statements in for initializer and update parts

[calixteman]

echo 'void f() {
    int i, j, k, l;
    for (i = 0, j = 0, k = 0, l = 0; i < 1; i++, j++, k++, l++) { }
}' | gcc -x c -c -

is working

[maxbrunsfeld]

Did comma_expression not work here? I would have thought it would work. I would also think that it would work for the initializer.

[calixteman]

You're right: I misread the recursive comma_expression.
And I thought it was better to have a "list" of initiliazers but when dumping the ast from clang, ',' is really a bin operator.

echo 'void f() {
    int i, j, k, l;
    for (i = 0, j = 0, k = 0, l = 0; i < 1; i++, j++, k++, l++) { }
}' | clang-9 -Xclang -ast-dump -x c -c -

So I'll update my patch.