Add hardfp flag to the Makefile.

This flag passes -Dv8_use_arm_eabi_hardfloat=true to gyp.

This is needed for Linux distros that are experimenting
with hardfp.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/10889026
Patch from Paweł Hajdan Jr. <phajdan.jr@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

Makefile

@@ -99,6 +99,10 @@ endif
 ifeq ($(regexp), interpreted)
   GYPFLAGS += -Dv8_interpreted_regexp=1
 endif
+# hardfp=on
+ifeq ($(hardfp), on)
+  GYPFLAGS += -Dv8_use_arm_eabi_hardfloat=true
+endif
 
 # ----------------- available targets: --------------------
 # - "dependencies": pulls in external dependencies (currently: GYP)