x86: don't suppress overflow diagnostics in x32 mode

x86: don't suppress overflow diagnostics in x32 mode

Unlike in 64-bit mode, where values wrap at the 64-bit boundary anyway,
there's no wrapping at the 32-bit boundary here, and hence overflow
detection shouldn't be suppressed just because rela relocations are
going to be used.

The extra check against NO_RELOC is actually a result of an ilp32 test
otherwise failing. But thinking about it, reporting overflows for
not-really-relocations (typically because of earlier errors) makes
little sense in general. Perhaps this should even be extended to non-
64-bit modes.