[DataLayout] Is non-byte ABI alignment on aggregate types supported?

The doc says:

This specifies the alignment for an object of aggregate type. <pref> is optional and defaults to <abi>.

However, all tests in codebase contain 0 and sometimes 8 in the abi part, which makes me wonder if the ABI alignment can be different from the byte width.
Should we explicitly disallow non-zero abi alignment and make pref alignment mandatory for aggregates?

FWIW When I try to set it to a different value, all I get is that clang crashes when calculating a structure layout.