Fix selecting the Platform in TargetList::CreateTargetInternal()

Summary:
TargetList::CreateTargetInternal() will only select the current Platform. A previous patch always sets platform_sp to the current Platform, so a check later to see if platform_sp was not defined always failed, and the current Platform was used. This patch removes that check, so if the current Platform is not compatible with the target architecture, CreateTargetInternal() will call Platform::GetPlatformForArchitecture() to select a compatible Platform.

Vince, remote linux tests (Ubuntu -> remote Ubuntu) pass the same with and without this patch.

Reviewers: vharron, clayborg

Reviewed By: clayborg

Subscribers: jingham, lldb-commits

Differential Revision: http://reviews.llvm.org/D8749

llvm-svn: 237053