[v27] Update build for iOS with x86_64 version for 64 bit simulator
[v27] Add arm64 architecture in double-conversion
[v27] Fix a problem in autoconf that ios_arch for simulator is forced to i386
[v27] Update configure
Merge pull request #27 from pandamicro/27_64bit

[v27] Support arm64 and x86_64 architecture for iOS 64 bit device and simulator
Merge branch 'master' of https://github.com/ricardoquesada/Spidermonkey

Conflicts:
	js/src/build-ios/build64.sh
	js/src/configure
Merge branch 'master' into v28
[v28] Build arm64 separately