Fixup gn check.

The new module clone tests require the WGSL reader and writer in order
to function. This Cl adds those dependencies to the BUILD.gn file.

Change-Id: I34cd9a7de13a99145bad1f559c23d181f4fb7739
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/34683
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Auto-Submit: dan sinclair <dsinclair@chromium.org>

.gn

@@ -14,8 +14,4 @@
 
 buildconfig = "//build/config/BUILDCONFIG.gn"
 
-check_targets = [
-  "//samples:*",
-  "//source:*",
-  "//third_party:*",
-]
+check_targets = [ "//:*" ]

BUILD.gn

@@ -841,6 +841,8 @@ source_set("tint_unittests_core_src") {
   deps = [
     ":gmock_and_gtest",
     ":libtint_core_src",
+    ":libtint_wgsl_reader_src",
+    ":libtint_wgsl_writer_src",
   ]
 }