stage2 extern union inside packed struct tripping LLVM assertion

[andrewrk]

zig version: 0.10.0-dev.2837+5735ce39a

Semantic Analysis [12517] test.complex.cabs... zig: /home/andy/Downloads/llvm-project-13/llvm/lib/IR/Constants.cpp:2225: static llvm::Constant* llvm::ConstantExpr::getBitCast(llvm::Constant*, llvm::Type*, bool): Assertion `CastInst::castIsValid(Instruction::BitCast, C, DstTy) && "Invalid constantexpr bitcast!"' failed.

Thread 1 "zig" received signal SIGABRT, Aborted.
0x00007ffff7aaabda in raise () from /nix/store/0xxjx37fcy2nl3yz6igmv4mag2a7giq6-glibc-2.33-123/lib/libc.so.6
(gdb) bt
#0  0x00007ffff7aaabda in raise () from /nix/store/0xxjx37fcy2nl3yz6igmv4mag2a7giq6-glibc-2.33-123/lib/libc.so.6
#1  0x00007ffff7a95533 in abort () from /nix/store/0xxjx37fcy2nl3yz6igmv4mag2a7giq6-glibc-2.33-123/lib/libc.so.6
#2  0x00007ffff7a9542f in __assert_fail_base.cold.0 () from /nix/store/0xxjx37fcy2nl3yz6igmv4mag2a7giq6-glibc-2.33-123/lib/libc.so.6
#3  0x00007ffff7aa3622 in __assert_fail () from /nix/store/0xxjx37fcy2nl3yz6igmv4mag2a7giq6-glibc-2.33-123/lib/libc.so.6
#4  0x00000000084468c5 in llvm::ConstantExpr::getBitCast (C=0x25e8d370, DstTy=0xf372f50, OnlyIfReduced=false) at /home/andy/Downloads/llvm-project-13/llvm/lib/IR/Constants.cpp:2225
#5  0x000000000846d6c8 in LLVMConstBitCast (ConstantVal=0x25e8d370, ToType=0xf372f50) at /home/andy/Downloads/llvm-project-13/llvm/lib/IR/Core.cpp:1766
#6  0x000000000104a26e in codegen.llvm.DeclGen.lowerValue (dg=0x7fffffff0470, tv=...) at /home/andy/Downloads/zig/src/codegen/llvm.zig:3322
#7  0x00000000015c2bd2 in codegen.llvm.FuncGen.resolveInst (self=0x7fffffff04b0, inst=377) at /home/andy/Downloads/zig/src/codegen/llvm.zig:3952
#8  0x00000000013dab5a in codegen.llvm.FuncGen.airStore (self=0x7fffffff04b0, inst=303) at /home/andy/Downloads/zig/src/codegen/llvm.zig:7192
#9  0x00000000013bc6be in codegen.llvm.FuncGen.genBody (self=0x7fffffff04b0, body=100 items at 0x25e8653c = {...}) at /home/andy/Downloads/zig/src/codegen/llvm.zig:4078
#10 0x00000000013b7c5c in codegen.llvm.Object.updateFunc (o=0xf36e610, module=0xf370f58, func=0x1db4d570, air=..., liveness=...) at /home/andy/Downloads/zig/src/codegen/llvm.zig:986
#11 0x00000000011b1138 in link.Elf.updateFunc (self=0xf371f30, module=0xf370f58, func=0x1db4d570, air=..., liveness=...) at /home/andy/Downloads/zig/src/link/Elf.zig:2369
#12 0x0000000000ffe70e in link.File.updateFunc (base=0xf371f30, module=0xf370f58, func=0x1db4d570, air=..., liveness=...) at /home/andy/Downloads/zig/src/link.zig:505
#13 0x0000000000fdd5b6 in Module.ensureFuncBodyAnalyzed (mod=0xf370f58, func=0x1db4d570) at /home/andy/Downloads/zig/src/Module.zig:3806
#14 0x0000000000d83beb in Compilation.processOneJob (comp=0xf36ff38, job=...) at /home/andy/Downloads/zig/src/Compilation.zig:2911
#15 0x0000000000d75c18 in Compilation.performAllTheWork (comp=0xf36ff38, main_progress_node=0x7fffffff21e0) at /home/andy/Downloads/zig/src/Compilation.zig:2843
#16 0x0000000000d6eb2e in Compilation.update (comp=0xf36ff38) at /home/andy/Downloads/zig/src/Compilation.zig:2218
#17 0x0000000000cfe0f0 in main.updateModule (gpa=..., comp=0xf36ff38, hook=...) at /home/andy/Downloads/zig/src/main.zig:3245
#18 0x0000000000c5a3d9 in main.buildOutputType (gpa=..., arena=..., all_args=4 items at 0xf36e278 = {...}, arg_mode=...) at /home/andy/Downloads/zig/src/main.zig:2934
#19 0x0000000000c07e87 in main.mainArgs (gpa=..., arena=..., args=4 items at 0xf36e278 = {...}) at /home/andy/Downloads/zig/src/main.zig:225
#20 0x0000000000c0761a in main (argc=4, argv=0x7fffffffa6d8) at /home/andy/Downloads/zig/src/stage1.zig:48
(gdb) 

Steps to reproduce: standard library tests on x86_64-linux with a debug LLVM.

pub const epoll_data = extern union {
    ptr: usize,
    fd: i32,
    @"u32": u32,
    @"u64": u64,
};
// On x86_64 the structure is packed so that it matches the definition of its
// 32bit counterpart
pub const epoll_event = switch (native_arch) {
    .x86_64 => packed struct {
        events: u32,
        data: epoll_data,
    },
    else => extern struct {
        events: u32,
        data: epoll_data,
    },
};