GN: Don't write ldflags and libs when unneeded.

tools/gn/ninja_binary_target_writer_unittest.cc

Index: tools/gn/ninja_binary_target_writer_unittest.cc
diff --git a/tools/gn/ninja_binary_target_writer_unittest.cc b/tools/gn/ninja_binary_target_writer_unittest.cc
index dc9c8ddf4373aab3b83a210ee97775e872d7d0e0..8aee945e33a9188fbde7c0f35c6f7d2d14de2deb 100644
--- a/tools/gn/ninja_binary_target_writer_unittest.cc
+++ b/tools/gn/ninja_binary_target_writer_unittest.cc
@@ -110,8 +110,6 @@ TEST(NinjaBinaryTargetWriter, SourceSet) {
         // There are no sources so there are no params to alink. (In practice
         // this will probably fail in the archive tool.)
         "build obj/foo/libstlib.a: alink || obj/foo/bar.stamp\n"
-        "  ldflags =\n"
-        "  libs =\n"
         "  output_extension = \n";
     std::string out_str = out.str();
     EXPECT_EQ(expected, out_str);
@@ -138,8 +136,6 @@ TEST(NinjaBinaryTargetWriter, SourceSet) {
         "build obj/foo/libstlib.a: alink obj/foo/bar.input1.o "
             "obj/foo/bar.input2.o ../../foo/input3.o ../../foo/input4.obj "
             "|| obj/foo/bar.stamp\n"
-        "  ldflags =\n"
-        "  libs =\n"
         "  output_extension = \n";
     std::string out_str = out.str();
     EXPECT_EQ(expected, out_str);