Rework v8_target_arch / target_cpu approach to use v8_target_cpu.

build/config/mips.gni

Index: build/config/mips.gni
diff --git a/build/config/mips.gni b/build/config/mips.gni
index cc6d53f8bebe2843aeb4817580019515410bb409..e23e74885919cb113792c536c2763e8b691761ef 100644
--- a/build/config/mips.gni
+++ b/build/config/mips.gni
@@ -2,7 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-if (current_cpu == "mipsel" || target_cpu == "mipsel") {
+import("//build/config/v8_target_cpu.gni")
+
+# These are primarily relevant in current_cpu == "mips*" contexts, where
+# MIPS code is being compiled.  But they can also be relevant in the
+# other contexts when the code will change its behavior based on the
+# cpu it wants to generate code for.
+if (current_cpu == "mipsel" || v8_target_cpu == "mipsel") {
   declare_args() {
     # MIPS arch variant. Possible values are:
     #   "r1"
@@ -27,7 +33,7 @@ if (current_cpu == "mipsel" || target_cpu == "mipsel") {
     #   "fpxx": sets the GCC -mfpxx option.
     mips_fpu_mode = "fp32"
   }
-} else if (current_cpu == "mips64el" || target_cpu == "mips64el") {
+} else if (current_cpu == "mips64el" || v8_target_cpu == "mips64el") {
   # MIPS arch variant. Possible values are:
   #   "r2"
   #   "r6"