Update ext/libv8/arch.rb

Check for arm. Compile still fails with
ERROR: Binary compiled with -mfloat-abi=hard but without -DUSE_EABI_HARDFLOAT
(raspberry pi)
Merge remote-tracking branch 'rtreffer/patch-1'.
Make arch detection more readable
Avoid compilation failure in snapshot
Tweak make flags to allow arm compilation
Avoid false positive for x86_64
Merge branch 'arm-native'

This commit fixes #42