[Issue 12751] Avoid heap allocations in some cases of array concatenation

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12751

--- Comment #1 from bearophile_hugs at eml.cc ---
Other basic cases that can be supported:

void main() @nogc {
    int[2] a = [10, 20];
    int[3] b = [40, 50, 60];
    int[6] c = a ~ 30 ~ b;
}


Currently DMD 2.066alpha gives:

test.d(4,16): Error: cannot use operator ~ in @nogc function main
test.d(4,16): Error: cannot use operator ~ in @nogc function main

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