std: better definition for std.os.linux.epoll_event

The previous definition depends on a non-lang-spec-compliant memory
layout for packed structs, which happens to trigger #11989 in stage2.

This commit changes the struct to be an extern struct with an
align(4) field. However, stage1 cannot handle this, so conditional
compilation logic is used to select different struct definitions
depending on stage1 vs stage2.

This works around #11989 but does not solve the underlying problem -
putting an extern union inside a packed struct will still trigger the
assert.

After this, both stage1 and stage2 std lib tests run assertion-clean
with a debug LLVM 13.

0 files changed, 0 insertions, 0 deletions