Cleanup the iOS simulator code.

Fixes include:
- Don't say that "<arch>-apple-ios" is compatible with "<arch>-apple-macosx"
- Fixed DynamicLoaderMacOSXDYLD so specify an architecture that was converted solely from a cputype and subtype, just specify the file + UUID.
- Fixed PlatformiOSSimulator::GetSupportedArchitectureAtIndex() so it returns the correct archs
- Fixed SymbolFileDWARFDebugMap to load .o files correctly by just specifying the architecture without the vendor and OS now that "<arch>-apple-ios" is not compatible with "<arch>-apple-macosx" so we can load .o files correctly for DWARF with debug map
- Fixed the coded in TargetList::CreateTarget() so it does the right thing with an underspecified triple where just the arch is specified.