Add support to PlatformRemoteiOS, PlatformRemoteAppleWatch, and

PlatformRemoteAppleTV to check the target.exec-search-paths 
directories for files after looking in the SDK.  An additional
wrinkle is that the remote file path may be something like
".../UIFoundation.framework/UIFoundation" and in 
target.exec-search-paths we will have "UIFoundation.framework".
Looking for just the filename of the path is not sufficient -
we need to also look for it by the parent directories because
this may be a darwin bundle/framework like the UIFoundation
example.

We really need to make a PlatformRemoteAppleDevice and have
PlatformRemoteiOS, PlatformRemoteAppleWatch, and PlatformRemoteAppleTV
inherit from it.  These three classes are 98% identical code.

<rdar://problem/25976619> 

llvm-svn: 272635