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

src/arm/macro-assembler-arm.h

Index: src/arm/macro-assembler-arm.h
diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 93d4f585cf0c3e3710b51e48910fb058be0c8342..9856716f06f1292def92813beadacd0f5922a188 100644
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -855,6 +855,15 @@ class MacroAssembler: public Assembler {
   void set_allow_stub_calls(bool value) { allow_stub_calls_ = value; }
   bool allow_stub_calls() { return allow_stub_calls_; }
 
+  // EABI variant for double arguments in use.
+  bool use_eabi_hardfloat() {
+#if USE_EABI_HARDFLOAT
+    return true;
+#else
+    return false;
+#endif
+  }
+
   // ---------------------------------------------------------------------------
   // Number utilities