cmd/link: disable a DWARF testpoint on Windows pending investigation

Disable a portion of the TestDWARF testpoint for Windows using
c-archive buildmode, pending investigation of the issue at hand, so as
to get the longtest builder unblocked.

Updates #35512.

Change-Id: Ib72d82ceaa674b9a51da220fb8e225231d5c3433
Reviewed-on: https://go-review.googlesource.com/c/go/+/206557
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/link/dwarf_test.go

@@ -139,6 +139,13 @@ func testDWARF(t *testing.T, buildmode string, expectDWARF bool, env ...string)
 				}
 			}
 
+			// Until there is a fix for issue 35512, don't try to use
+			// SeekPC or look at the line table on Windows under
+			// c-archive build mode.
+			if buildmode == "c-archive" && runtime.GOOS == "windows" {
+				t.Skip("avoiding SeekPC until 35512 fixed")
+			}
+
 			// TODO: We'd like to use filepath.Join here.
 			// Also related: golang.org/issue/19784.
 			wantFile := path.Join(prog, "main.go")