Remove old references to cpu_arch, os from GN files.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
@@ skipping 555 matching lines @@
     }
 
     defines += [
       "USE_STLPORT=1",
       "_STLP_USE_PTR_SPECIALIZATIONS=1",
       "__GNU_SOURCE=1",  # Necessary for clone().
     ]
 
     # TODO(jdduke) Re-enable on mips after resolving linking
     # issues with libc++ (crbug.com/456380).
-    if (cpu_arch != "mipsel" && cpu_arch != "mips64el") {
+    if (current_cpu != "mipsel" && current_cpu != "mips64el") {
       ldflags += [ "-Wl,--warn-shared-textrel" ]
     }
     ldflags += [ "-nostdlib" ]
 
     # NOTE: The stlport header include paths below are specified in cflags
     # rather than include_dirs because they need to come after include_dirs.
     # Think of them like system headers, but don't use '-isystem' because the
     # arm-linux-androideabi-4.4.3 toolchain (circa Gingerbread) will exhibit
     # strange errors. The include ordering here is important; change with
     # caution.
@@ skipping 389 matching lines @@
   ]
   common_optimize_on_ldflags = []
 
   if (is_android) {
     if (!using_sanitizer) {
       common_optimize_on_cflags += [ "-fomit-frame-pointer" ]
     }
 
     # TODO(jdduke) Re-enable on mips after resolving linking
     # issues with libc++ (crbug.com/456380).
-    if (cpu_arch != "mipsel" && cpu_arch != "mips64el") {
+    if (current_cpu != "mipsel" && current_cpu != "mips64el") {
       common_optimize_on_ldflags += [
         # Warn in case of text relocations.
         "-Wl,--warn-shared-textrel",
       ]
     }
   }
 
   if (is_mac) {
     if (symbol_level == 2) {
       # Mac dead code stripping requires symbols.
@@ skipping 113 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }