cmd/link/internal/ld: fix external linking on windows

gcc on windows writes invalid location for .debug_gdb_scripts
which causes the executable loading to fail.

Fixes #20183

Change-Id: I5134013bc926b44a55b528f66ab79555855d1f4d
Reviewed-on: https://go-review.googlesource.com/42651Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1448,6 +1448,11 @@ func writearanges(ctxt *Link, syms []*Symbol) []*Symbol {
 }
 
 func writegdbscript(ctxt *Link, syms []*Symbol) []*Symbol {
+	if Linkmode == LinkExternal && Headtype == objabi.Hwindows {
+		// gcc on Windows places .debug_gdb_scripts to a wrong location
+		// which causes program not to run. See https://golang.org/issue/20183
+		return syms
+	}
 
 	if gdbscript != "" {
 		s := ctxt.Syms.Lookup(".debug_gdb_scripts", 0)