cmd/link: set .ctors COFF section to writable and aligned

Without setting these flags, LLVM's LLD ignores the .ctors section when
merging objects.

Updates #44250.
Updates #39326.
Updates #38755.
Updates #36439.
Updates #43800.

Change-Id: I8766104508f7acd832088a590ee7d68afa0d6065
Reviewed-on: https://go-review.googlesource.com/c/go/+/291633


Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>