Parse extern (a, b) = ...; and scope (a, b) = ...;.

[tgehr]

Quirin talked a bit about ambiguity issues with his primary type DIP today and we noticed that my unpacking parser has some missing cases (there is no ambiguity, but a lot of similar cases are tricky):

extern (a, b) = tuple (1, 2); // parser thinks this is a linkage declaration

void main(){
    scope (a, b) = tuple(1, 2); // parser thinks this is a scope guard
}

This patch fixes both of those parsing issues, by detecting the = after the parentheses. This is not very important for extern, as extern declarations do not support initializers anyway, but parsing it correctly does improve the error message.

[adamdruppe]

sweet thx