Update the nacl_bootstrap GN code to work in ChromeOS chroot builds.

src/trusted/service_runtime/linux/BUILD.gn

Index: src/trusted/service_runtime/linux/BUILD.gn
diff --git a/src/trusted/service_runtime/linux/BUILD.gn b/src/trusted/service_runtime/linux/BUILD.gn
index 37cc61fa1059ed8af6cc12fc2c86235f8eed72cd..52c298246d60096945aa021542738348a6b4bcc6 100644
--- a/src/trusted/service_runtime/linux/BUILD.gn
+++ b/src/trusted/service_runtime/linux/BUILD.gn
@@ -15,8 +15,20 @@
 # Gold for the link, so use_gold=true is a false statement and might
 # cause other problems.
 
-here = get_label_info(".", "dir")
-bootstrap_toolchain = here + "/toolchain:nacl_bootstrap_" + target_cpu
+# TODO(dpranke): There needs to be a better way to determine if
+# we are using the custom CrOS toolchains, but for now we check is_clang,
+# which is the same way we check in //build/config/BUILDCONFIG.gn.

[Roland McGrath, 2016/06/22 19:29:48]

If the same check is done in BUILDCONFIG.gn already, then why not have that set
the variable and just use it here?

Or else, put the magic into cros_toolchain.gni so here we can just import that
and test variables it sets.

It seems pretty nasty to have fiddly logic like this here rather than somewhere
in build/.

+if (target_os == "chromeos") {
+  import("//build/toolchain/cros_toolchain.gni")
+  _is_cros_target_toolchain = !is_clang
+}
+
+if (_is_cros_target_toolchain) {
+  bootstrap_toolchain = "//build/toolchain/cros:nacl_bootstrap"
+} else {
+  here = get_label_info(".", "dir")
+  bootstrap_toolchain = here + "/toolchain:nacl_bootstrap_" + target_cpu
+}
 
 if (current_toolchain == bootstrap_toolchain) {
   bootstrap_lib_path = "$target_out_dir/libnacl_bootstrap_lib.a"
@@ -42,7 +54,9 @@ if (current_toolchain == bootstrap_toolchain) {
     linker_emulation = "elf32ltsmip"
   }
 
-  if (is_android) {
+  if (_is_cros_target_toolchain) {
+    compiler = cros_target_cxx
+  } else if (is_android) {
     compiler = "g++"
   } else if (current_cpu == "arm") {
     compiler = "arm-linux-gnueabihf-g++"
@@ -50,11 +64,6 @@ if (current_toolchain == bootstrap_toolchain) {
     compiler = "g++"
   }
 
-  if (target_os == "chromeos" && defined(cros_target_cxx) &&

[Dirk Pranke, 2016/06/22 01:38:27]

This shouldn't have really worked before, since cros_target_cxx wasn't
technically in scope. Now, we do pull in the right cros_target_cxx value, but
that's always non-empty, so we can't check it to see if we need to use a custom
value.

Instead, we duplicate the logic in BUILDCONFIG.gn, and end up getting the same
"g++" value, since that is the default either way.

-      cros_target_cxx != "") {
-    compiler = cros_target_cxx
-  }
-
   static_library("nacl_bootstrap_lib") {
     # This code has very specific requirements related to its static
     # linking and minimal libc use.  It cannot support the normal variety