[Issue 24029] New: ImportC: symbol name clash on statement expressions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24029

          Issue ID: 24029
           Summary: ImportC: symbol name clash on statement expressions
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: dkorpel at live.nl

Found in the test case of https://github.com/dlang/dmd/pull/15375 with multiple
asserts. Reduced:

```C
int x = 0;
int y = 0;

void a()
{
    (__extension__ ({ x += 2; })); // test.a.__dgliteral1
}

void b()
{
    (__extension__ ({ y += 1; })); // test.b.__dgliteral1
}

int main(void)
{
    a();
    b();
    __check(x == 2);
    __check(y == 1);
    return 0;
}
```

Output:
```
/usr/bin/ld: warning: size of symbol `__dgliteral1' changed from 20 in test.o
to 19 in test.o
```

And the test fails. Because it's ImportC, the __dgliteral symbols don't get
their function as a prefix in the mangle, so the symbols clash.

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