GN: support 32-bit x86 builds

gn/BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
   ar = "ar"
   cc = "cc"
   cxx = "c++"
 
@@ skipping 21 matching lines @@
   # It's annoying to wait for full debug symbols to push over
   # to Android devices.  -gline-tables-only is a lot slimmer.
   if (is_android) {
     cflags = [ "-gline-tables-only" ]
   } else {
     cflags = [ "-g" ]
   }
 }
 
 config("default") {
+  asmflags = []
   cflags = [
     "-O1",
     "-fstrict-aliasing",
     "-fPIC",
     "-fvisibility=hidden",
 
     "-Werror",
     "-Wall",
     "-Wextra",
     "-Winit-self",
@@ skipping 18 matching lines @@
     cflags += [
       "-march=armv7-a",
       "-mfpu=neon",
       "-mthumb",
     ]
   } else if (current_cpu == "mipsel") {
     cflags += [
       "-march=mips32r2",
       "-mdspr2",
     ]
+  } else if (current_cpu == "x86") {
+    asmflags += [ "-m32" ]
+    cflags += [
+      "-m32",
+      "-msse2",
+      "-mfpmath=sse",
+    ]
+    ldflags += [ "-m32" ]
   }
 
   if (is_android) {
-    asmflags = [
+    asmflags += [
       "--target=$ndk_target",
       "-B$ndk/toolchains/$ndk_gccdir-4.9/prebuilt/$ndk_host/$ndk_target/bin",
     ]
     cflags += [
       "--sysroot=$ndk/platforms/$ndk_platform",
       "--target=$ndk_target",
       "-B$ndk/toolchains/$ndk_gccdir-4.9/prebuilt/$ndk_host/$ndk_target/bin",
     ]
     cflags_cc += [
       "-isystem$ndk/sources/android/support/include",
@@ skipping 139 matching lines @@
   }
 
   tool("stamp") {
     command = "touch {{output}}"
   }
 
   tool("copy") {
     command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
   }
 }