Only build arm64 if 7.0 SDK is present

Conflicts:
	scripts/prepare-libetpan-ios.sh
	scripts/prepare-tidy-ios.sh
Added arm64 support

Conflicts:
	build-mac/mailcore2.xcodeproj/project.pbxproj
	scripts/prepare-libetpan-ios.sh
	scripts/prepare-tidy-ios.sh
build for arm64 for dependencies