Clarify arm gn configuration

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 827cd2c366bbdf2a7c4d3cf8792a78b102b7ee2c..f1854afa9209cdb76c12a49af2aac860ea5ba156 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -124,14 +124,12 @@ config("toolchain") {
       }
       if (arm_fpu == "vfpv3-d16") {
         defines += [ "CAN_USE_VFP3_INSTRUCTIONS" ]
-      }
-      if (arm_fpu == "vfpv3") {
+      } else if (arm_fpu == "vfpv3") {
         defines += [
           "CAN_USE_VFP3_INSTRUCTIONS",
           "CAN_USE_VFP32DREGS",
         ]
-      }
-      if (arm_fpu == "neon") {
+      } else if (arm_fpu == "neon") {
         defines += [
           "CAN_USE_VFP3_INSTRUCTIONS",
           "CAN_USE_VFP32DREGS",
@@ -139,6 +137,7 @@ config("toolchain") {
         ]
       }
     } else {
+      # These defines ares used for the ARM simulator.

[jochen (gone - plz use gerrit), 2015/03/13 07:42:51]

it's not just for the snapshot toolchain - we could target_cpu == x86 and
v8_target_arch == arm

[Dirk Pranke, 2015/03/13 20:47:17]

Um, okay ... I guess I don't understand what this is fully yet, and need to look
into where else (or how else) v8_target_arch is used.

       defines += [
         "CAN_USE_ARMV7_INSTRUCTIONS",
         "CAN_USE_VFP3_INSTRUCTIONS",