cmd/link: writelines should keep is_stmt in sync with what it's writing

For all functions but the last one if the function ends on a
non-statement instruction the statement flag in debug_line is changed
but is_stmt is not updated to match.

Change-Id: I03c275c5e261ea672ce4da7baca2458810708326
Reviewed-on: https://go-review.googlesource.com/112979Reviewed-by: David Chase <drchase@google.com>

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

@@ -1302,6 +1302,7 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
 		}
 		if is_stmt == 0 && i < len(textp)-1 {
 			// If there is more than one function, ensure default value is established.
+			is_stmt = 1
 			ls.AddUint8(uint8(dwarf.DW_LNS_negate_stmt))
 		}
 	}