Avoid importing nacl config for non-NaCl toolchains.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index c2f9aff2757a915d06b56aa04890bbb7d944a2fd..5ea23c5ef3e1e05ceda1aea8df2c1505c23e4853 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -6,7 +6,6 @@ import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
-import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build_overrides/build.gni")
@@ -23,6 +22,12 @@ if (is_mac) {
 if (is_ios) {
   import("//build/config/ios/ios_sdk.gni")
 }
+if (is_nacl) {
+  # To keep NaCl variables out of builds that don't include NaCl, all
+  # variables defined in nacl/config.gni referenced here should be protected by
+  # is_nacl conditions.
+  import("//build/config/nacl/config.gni")
+}
 
 declare_args() {
   # Default to warnings as errors for default workflow, where we catch
@@ -1494,7 +1499,7 @@ config("no_optimize") {
 # optimization and link-time code generation which is very expensive and should
 # be used sparingly.
 config("optimize_max") {
-  if (is_nacl_irt) {
+  if (is_nacl && is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # Various components do:
     #   if (!is_debug) {
@@ -1541,7 +1546,7 @@ config("optimize_max") {
 # TODO(crbug.com/621335) - rework how all of these configs are related
 # so that we don't need this disclaimer.
 config("optimize_speed") {
-  if (is_nacl_irt) {
+  if (is_nacl && is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # Various components do:
     #   if (!is_debug) {
@@ -1587,7 +1592,7 @@ config("optimize_fuzzing") {
 # The default optimization applied to all targets. This will be equivalent to
 # either "optimize" or "no_optimize", depending on the build flags.
 config("default_optimization") {
-  if (is_nacl_irt) {
+  if (is_nacl && is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # It gets optimized the same way regardless of the type of build.
     configs = [ "//build/config/nacl:irt_optimize" ]