cmd/link/internal/ld: align PE .text section to 32-byte when external linking

Some symbols, for example, masks requires 16-byte alignment, and
they are placed in the text section. Before this change, the text
section is only aligned to 4-byte, and it's making masks unaligned.

Fixes #12415.

Change-Id: I7767778d1b4f7d3e74c2719a02848350782a4160
Reviewed-on: https://go-review.googlesource.com/14166
Run-TryBot: Minux Ma <minux@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -1107,6 +1107,11 @@ func Asmbpe() {
 
 	t := addpesection(".text", int(Segtext.Length), int(Segtext.Length))
 	t.Characteristics = IMAGE_SCN_CNT_CODE | IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ
+	if Linkmode == LinkExternal {
+		// some data symbols (e.g. masks) end up in the .text section, and they normally
+		// expect larger alignment requirement than the default text section alignment.
+		t.Characteristics |= IMAGE_SCN_ALIGN_32BYTES
+	}
 	chksectseg(t, &Segtext)
 	textsect = pensect