When generating tbaa.struct metadata we treat multiple adjacent
bitfields as a single "field", with one corresponding entry in the
metadata. At the moment this is achieved by adding an entry for the
first bitfield in the run using its StorageSize and skipping the
remaining bitfields. The problem is that "first" is determined by
checking that the Offset of the field in the run is 0, which breaks for
big endian.
PR: https://github.com/llvm/llvm-project/pull/87753
This test exposes what I think is invalid tbaa.struct metadata currently
generated for bitfields when using big endian layout. The regions given
by `!{i64 2, i64 4, [[META3:![0-9]+]], i64 4, i64 4 ...` are
overlapping. This issue was originally observed in
https://github.com/llvm/llvm-project/pull/86709.
