LLVM backend miscompilation, assigning packed struct pointer to global zeroes it

### Zig Version 0.15.1 ### Steps to Reproduce and Observed Behavior I have a packed struct that contains a pointer. If I assign it to a new value, and that value points to a global, the LLVM backend zeroes the struct. The x64 backend compiles it correctly. ### Expected Behavior I expected this test to pass on both backends: ```zig var global_var: u32 = 10; const PackedStruct = packed struct { ptr: *u32, }; test "foo" { const instance: PackedStruct = .{ .ptr = &global_var }; var copy: PackedStruct = undefined; copy = instance; try std.testing.expectEqual(instance.ptr, copy.ptr); } ``` But I get this output on the LLVM backend: ```zig error: 'ext.tag.test.foo' failed: expected u32@1127248, found u32@0 ```