stdlib: fix compilation errors in stdlib

[nurmukhametov]

All of them caused by unbound casting diagnostic.
Under --debug there are quite a few errors reported: E.g., on atomic swaps, ispc reported:

Error: Unable to find any matching overload for call to function (/*unbound*/ int64 * uniform, varying int64)

This PR allows to use --debug for compilation with enabled stdlib.

[aneshlya]

Seems like it stopped working after v1.18.0 but I don't remember any user-visible changes about unbound variability. I recommend finding the commit after which it stopped working. It's possible that the change wasn't implemented correctly. The same problem can be easily reproduced in the user's code, even without the stdlib.

[nurmukhametov]

Yes, indeed. Consider the following reproducer:

void foo(void *uniform dst, void *uniform src, uniform int32 count) {
    __memcpy32((int8 * uniform) dst, (int8 * uniform) src, count);
}

Run with --debug and --nostdlib:

$ ./bin/ispc t2.ispc -o t.o -O2 --target=avx2-i32x8 --debug --nostdlib
Initial AST
`-Function <t2.ispc:2.5 - 2.67>  "foo"
  `-(body) StmtList <t2.ispc:2.5 - 2.67>
    `-ExprStmt <t2.ispc:2.5 - 2.66>
t2.ispc:2:5: Error: Unable to find any matching overload for call to function "__memcpy32" only considering exact matches.
        Passed types: (/*unbound*/ int8 * uniform, /*unbound*/ int8 * uniform, uniform int32)

    __memcpy32((int8 * uniform) dst, (int8 * uniform) src, count);
    ^^^^^^^^^^

on v1.18.0 fails but good for v1.17.0.

Bisecting between these revisions shows that the guilty PR is #2299.

The underlying cause is not clear for me, because somehow AST dumping functionality interferes with type checking and function overloads resolving, e.g. commenting out this line

ispc/src/func.cpp

Line 201 in 9be6bd6

debugPrintHelper(DebugPrintPoint::Initial);

made error gone.