Build PPAPI NaCl Glibc tests with GN

ppapi/native_client/BUILD.gn

Index: ppapi/native_client/BUILD.gn
diff --git a/ppapi/native_client/BUILD.gn b/ppapi/native_client/BUILD.gn
index 23a23714d3f565a73ab83951cd18bb0cfc69a654..d131180aabc7caa70f8b82401a244d3d75f662b8 100644
--- a/ppapi/native_client/BUILD.gn
+++ b/ppapi/native_client/BUILD.gn
@@ -3,13 +3,17 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
+import("//build/config/nacl/config.gni")
 
 if (is_nacl) {
   group("ppapi_lib") {
     deps = [
-      "//native_client/src/untrusted/pthread",
       "//ppapi/native_client/src/untrusted/irt_stub:ppapi_stub_lib",
     ]
+    if (!is_nacl_glibc) {
+      # Glibc has its version of pthread library.
+      deps += [ "//native_client/src/untrusted/pthread" ]
+    }
   }
 
   executable("nacl_irt") {