Fix bug in Linux remote dynamic loader setup and fix test.

Part 1 changes PlatformLinux::CreateInstance to always create with
is_host=false; that method is only used as the plug-in creator method
associated with the remote-linux platform plugin, and should therefore
always be remote.

Part 1 patch by Steve Pucci.

Part 2: fix a test break on linux.

In test/functionalities/thread/thread_specific_break, when using gcc,
either C99 mode would need to be enabled, or the code would need to
change.  I changed a couple loop variable definitions to conform
to pre-C99 to simplify testing the fix.  The second issue was
the necessity to include -lpthread as a linker option in the Makefile.

Any issues with that part are due to me (Todd Fiala).