cmd/link: enable DWARF compression on Windows

Simple follow-on to CL 118276. Everything worked except that the
compressed sections need to be aligned at PEFILEALIGN.

Fixes #25927
Updates #11799

Change-Id: Iec871defe30e3e66055d64a5ae77d5a7aca355f5
Reviewed-on: https://go-review.googlesource.com/119816
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/link/internal/ld/dwarf.go

@@ -1951,7 +1951,7 @@ func dwarfaddelfsectionsyms(ctxt *Link) {
 // relocations are applied. After this, dwarfp will contain a
 // different (new) set of symbols, and sections may have been replaced.
 func dwarfcompress(ctxt *Link) {
-	if !ctxt.IsELF || ctxt.LinkMode == LinkExternal {
+	if !(ctxt.IsELF || ctxt.HeadType == objabi.Hwindows) || ctxt.LinkMode == LinkExternal {
 		return
 	}
 
@@ -1998,6 +1998,10 @@ func dwarfcompress(ctxt *Link) {
 			log.Fatalf("%s: unexpected sub-symbols", s)
 		}
 		pos += uint64(s.Size)
+		if ctxt.HeadType == objabi.Hwindows {
+			pos = uint64(Rnd(int64(pos), PEFILEALIGN))
+		}
+
 	}
 	Segdwarf.Length = pos - Segdwarf.Vaddr
 }