It looks like the compiler is failing this conditional in perl_math_int128.c:

#if ((LONGSIZE >= 8) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINO
+R__ >= 4)))
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__GNUC__ is 4 and __GNUC_MINOR__ is 2. However, Math::Int128 itself compiles and tests successfully. Removing the conditional above fixes the problem but I'd like to understand a bit more why it's there in the first place.

edit: just to be clear, the compiler in question is clang

Matt