Change Linux Platform to support non-host Linux architectures

Summary:
This was originally http://reviews.llvm.org/D8709 , but I didn't commit it correctly. 

Since then GetSupportedArchitectureAtIndex() has been changed. That change, http://reviews.llvm.org/D9511 , breaks non-x86 linux implementations, so this change goes back to the old implementation and adds remote linux support from D8709.

D8709 summary:

The Linux Platform currently will only say the Host architecture is supported. This patch retains that behavior for the Host Platform, but adds a list of architectures for the Remote Platform.


Reviewers: clayborg, flackr

Reviewed By: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9683

llvm-svn: 237278