cmd/link: use correct alignment in PE DWARF sections

Set the correct section flags to insure that .debug_* sections are
using 1-byte alignment instead of the default. This seems to be
important for later versions of LLVM-mingw on windows (shows up on the
windows/arm64 builder).

Updates #46406.

Change-Id: I023d5208374f867552ba68b45011f7990159868f
Reviewed-on: https://go-review.googlesource.com/c/go/+/324763


Trust: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>