ARM: Support hardfloat in SCons build and make it a build time setting

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index fc417ef3823c979463467228fa8d70ef0ac0a7ef..725008a784c531c139117e5c86a35372c5fcc4fa 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -294,6 +294,10 @@ class OS {
   // Support runtime detection of VFP3 on ARM CPUs.
   static bool ArmCpuHasFeature(CpuFeature feature);
 
+  // Support runtime detection of whether the hard float option of the
+  // EABI is used.
+  static bool ArmUsingHardFloat();
+
   // Support runtime detection of FPU on MIPS CPUs.
   static bool MipsCpuHasFeature(CpuFeature feature);