Update from https://crrev.com/318214

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index cd107305d6e42018c2c40879f76cc392fc04dbbb..7c06e5934c8c53a569df09179c8bfa5f0cd62ac5 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -121,6 +121,7 @@ declare_args() {
 }
 
 # TODO(dpranke): Remove these asserts when os and cpu_arch are removed.
+assert(current_cpu == cpu_arch)
 assert(current_os == os)
 
 # =============================================================================
@@ -547,6 +548,12 @@ if (is_win) {
 } else if (is_ios) {
   host_toolchain = "//build/toolchain/mac:host_clang"
   set_default_toolchain("//build/toolchain/mac:clang")
+} else if (is_nacl) {
+  # TODO(GYP): This will need to change when we get NaCl working
+  # on multiple platforms, but this whole block of code (how we define
+  # host_toolchain) needs to be reworked regardless to key off of build_os
+  # and build_cpu_arch rather than the is_* variables.
+  host_toolchain = "//build/toolchain/linux:clang_x64"
 }
 
 # ==============================================================================