Add support for iOS8 in the build scripts

When building MailCore for the first time with XCode6 and iOS8, the project fails to build, as a number of scripts fail with an "SDK Not Found" error.  This PR adds a check for iOS8 to the relevant scripts, which allows MailCore to build with no problems.
Could you change it to `archs="armv7 armv7s arm64 i386 x86_64"`