ARM: Make use of d16-d31 when available.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 824cabe420821882d4d53ebb3f7d731ae53bdcfa..3a596399d69686d32a4ffe9e26849244f59264e5 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -51,6 +51,13 @@
     'v8_can_use_vfp2_instructions%': 'false',
     'v8_can_use_vfp3_instructions%': 'false',
 
+    # Setting 'v8_can_use_vfp32dregs' to 'true' will cause V8 to use the VFP
+    # registers d16-d31 in the generated code, both in the snapshot and for the
+    # ARM target. Leaving the default value of 'false' will avoid the use of
+    # these registers in the snapshot and use CPU feature probing when running
+    # on the target.
+    'v8_can_use_vfp32dregs%': 'false',
+
     # Similar to vfp but on MIPS.
     'v8_can_use_fpu_instructions%': 'true',
 
@@ -178,6 +185,11 @@
               'USE_EABI_HARDFLOAT=0',
             ],
           }],
+          [ 'v8_can_use_vfp32dregs=="true"', {
+            'defines': [
+              'CAN_USE_VFP32DREGS',
+            ],
+          }],
         ],
       }],  # v8_target_arch=="arm"
       ['v8_target_arch=="ia32"', {