[Issue 18232] Union methods fail to initialize local variables to .init

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18232

--- Comment #4 from hsteoh at quickfur.ath.cx ---
More interesting clues: running a union method inside CTFE containing a local
variable without an explicit initializer causes a CTFE error "cannot modify
variable at compile time", whereas explicitly initializing the local variable
works.

------
union U {
    int method() {
        int x; // causes CTFE failure unless explicitly initialized
        return x;
    }
}
enum y = U.init.method();
------

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