ios: improve kit and toolchains autodetection

* simplify probe
* adapt to Xcode 5.0.1 (32->64 bits)
* force correct abi for iphonesimulator (autodetection fails)

Change-Id: Ib489d621858fd1b026222f067245a0480ea8fa03
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>