iOS build configuration updates.
Commit message longer than commit edition. Simulator and devices: Add a common minimum iOS version that can be shared by iOS and iOS simulator targets. Fix --enable-debug (for device targets; sim was fine): Allow for successful configuration and build with --enable-debug when CXX is available by: - Using CXX as LD (when CXX is available). - Passing the correct form of the iOS minimum version parameter based on whether LD is CXX or really is ld. Note: ld -g still won't work on macosx with this patch, so if CXX is not available, configuration will still fail reporting that the toolchain cannot link executables when attempting to pass --enable-debug (because ld returns an error code since the one included with xcode doesn't support the -g argument). Change-Id: Ia488aed167cc2ca82ee9e980589fb76dddce634f