Land prep work to enable NaCl in the Linux x64 GN builds.

mojo/nacl/BUILD.gn

Index: mojo/nacl/BUILD.gn
diff --git a/mojo/nacl/BUILD.gn b/mojo/nacl/BUILD.gn
index 3ce017d44c0cca6eb33e44cdfa62bff98430ec9f..e15035a0b34d94291e5cd63c3614532e9efc6533 100644
--- a/mojo/nacl/BUILD.gn
+++ b/mojo/nacl/BUILD.gn
@@ -33,6 +33,9 @@ if (!is_nacl) {
       "$gen_dir/mojo_syscall.cc",
       "monacl_sel_main.cc",
     ]
+
+    include_dirs = [ "//third_party/mojo/src" ]
+
     deps = [
       # This target makes sure we have all the pre-processor defines needed to
       # use NaCl's headers.
@@ -68,6 +71,7 @@ if (is_nacl) {
     deps = [
       ":mojo_nacl_codegen($default_toolchain)",
     ]
+    include_dirs = [ "//third_party/mojo/src" ]
   }
 
   # Unit test for the Mojo public API.
@@ -77,6 +81,7 @@ if (is_nacl) {
       "//third_party/mojo/src/mojo/public/cpp/system/tests/core_unittest.cc",
       "//third_party/mojo/src/mojo/public/cpp/system/tests/macros_unittest.cc",
     ]
+    include_dirs = [ "//third_party/mojo/src" ]
     deps = [
       "//native_client/src/untrusted/nacl:imc_syscalls",
       "//testing/gtest:gtest",