Add khronos_glcts_test to both_gn_and_gyp target

This will allow us to re-enable internal_khronos_glcts_tests in
chromeos-chrome-9999.ebuild if we need to.

BUG=607669

Review-Url: https://codereview.chromium.org/1954263002
Cr-Commit-Position: refs/heads/master@{#392173}

diff --git a/BUILD.gn b/BUILD.gn
index bf1f75d..f771e1b 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -146,6 +146,7 @@
       "//extensions:extensions_browsertests",
       "//extensions:extensions_unittests",
       "//gpu/gles2_conform_support:gles2_conform_test",
+      "//gpu/khronos_glcts_support:khronos_glcts_test",
       "//jingle:jingle_unittests",
       "//net:hpack_example_generator",
       "//net:hpack_fuzz_mutator",