The beginnings of a gtest-based test framework.

Makes use of LLVM gtest support.  This does *not* run as part of
the lldb test suite.

I'm using it to start testing some components that
I'll be adding to the inner guts of NativeThreadLinux to more
maintainably handle thread states and deferred thread state notification.

Runs with default Makefile target "test" using gmake within a given
test directory (currently only test/c++/native_process/thread_state_coordinator).

The Makefile.rules currently assume it is using the LLVM gtest.  It works on
a canonical MacOSX dir structture (i.e. lldb, lldb/llvm, lldb/llvm/tools/clang).
It also works on Ubuntu assuming the standard dir layout of llvm, llvm/tools/clang,
llvm/tools/lldb.  In this case, it expects a directory called build-debug parallel
to the llvm source dir.  All directory assumptions can be overridden with
environment variables.  See test/c++/make/Makefile.rules for details.

We'll want to make this smarter in the future, particularly around finding the LLVM build
output dir.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218422 91177308-0d34-0410-b5e6-96231b3b80d8
Moved PlatformDarwin::GetEnvironment() to PlatformPOSIX to fix Linux/llgs issue.

See http://reviews.llvm.org/D5486 for more details.

I was tracking a problem where llgs on linux would not pick up any environment variables. On OSX there is a virtual function PlatformDarwin::GetEnvironment() which correctly sets up the list of environment variables. On linux llgs it defaults to a base class default implementation which clears the list.

I moved the OSX implementation down to PlatformPOSIX. This fixes my problem on linux still works properly on OSX.

Change by Shawn Best.
Slight tweak to convert 'virtual' to 'override' in PlatformDarwin.h virtual method override by Todd.

Tested:
Ubuntu 14.04 x86_64, cmake/ninja build + tests.
MacOSX 10.9.5 x86_64, Xcode 6.1 Beta build + tests.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218424 91177308-0d34-0410-b5e6-96231b3b80d8