Fix the GN build for MIPS.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 509d78afea11a1e700d3fa040092a98c14fa7b68..ab1e094ce273c65fc35f3edac9a9c140ba8c1129 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -113,7 +113,7 @@ config("toolchain") {
   defines = []
   cflags = []
 
-  # TODO(jochen): Add support for arm subarchs, mips, mipsel.
+  # TODO(jochen): Add support for arm subarchs, mips, mipsel, mips64el.

[Dirk Pranke, 2015/03/17 21:44:13]

I think this is completely appropriate. 

lgtm.

 
   if (v8_target_arch == "arm") {
     defines += [ "V8_TARGET_ARCH_ARM" ]
@@ -150,6 +150,12 @@ config("toolchain") {
   if (v8_target_arch == "arm64") {
     defines += [ "V8_TARGET_ARCH_ARM64" ]
   }
+  if (v8_target_arch == "mipsel") {
+    defines += [ "V8_TARGET_ARCH_MIPS" ]
+  }
+  if (v8_target_arch == "mips64el") {
+    defines += [ "V8_TARGET_ARCH_MIPS64" ]
+  }
   if (v8_target_arch == "x86") {
     defines += [ "V8_TARGET_ARCH_IA32" ]
   }