Auto merge of #38670 - dotdash:transmute_align, r=eddyb

Fix transmute::<T, U> where T requires a bigger alignment than U

For transmute::<T, U> we simply pointercast the destination from a U
pointer to a T pointer, without providing any alignment information,
thus LLVM assumes that the destination is aligned to hold a value of
type T, which is not necessarily true. This can lead to LLVM emitting
machine instructions that assume said alignment, and thus cause aborts.

To fix this, we need to provide the actual alignment to store_operand()
and in turn to store() so they can set the proper alignment information
on the stores and LLVM can emit the proper machine instructions.

Fixes #32947

src/librustc_trans/mir/mod.rs

@@ -515,7 +515,7 @@ fn arg_local_refs<'a, 'tcx>(bcx: &BlockAndBuilder<'a, 'tcx>,
             // environment into its components so it ends up out of bounds.
             let env_ptr = if !env_ref {
                 let alloc = bcx.fcx().alloca(common::val_ty(llval), "__debuginfo_env_ptr");
-                bcx.store(llval, alloc);
+                bcx.store(llval, alloc, None);
                 alloc
             } else {
                 llval