Make changes for cmake based build of hexagon_remote (#237)

* Make changes for cmake based build of hexagon_remote

- Change HL_HEXAGON_SIM_REMOTE and LD_LIBRARY_PATH to reflect new locations
of hexagon_sim_remote and libhalide_hexagon_host.so respectively.
- Add HEXAGON_SDK_ROOT to point to the toplevel of the Hexagon SDK

* Build the Hexagon backend in LLVM only if the builder handles hexagon

* Fix a bad merge

master/master.cfg

@@ -840,15 +840,14 @@ def add_env_setup_step(factory, builder_type, enable_ccache=False):
 
     if builder_type.handles_hexagon():
         # Environment variables for testing Hexagon DSP
-        hexagon_remote_bin = get_halide_source_path('src', 'runtime', 'hexagon_remote', 'bin')
-
+        hexagon_remote_bin = get_halide_build_path('src', 'runtime', 'hexagon_remote')
         # Assume that HL_HEXAGON_TOOLS points to the correct directory (it might not be /usr/local/hexagon)
-        env['HL_HEXAGON_SIM_REMOTE'] = Transform(os.path.join, hexagon_remote_bin, 'v65', 'hexagon_sim_remote')
+        env['HL_HEXAGON_SIM_REMOTE'] = Transform(os.path.join, hexagon_remote_bin, 'hexagon', 'bin', 'hexagon_sim_remote')
         env['HL_HEXAGON_SIM_CYCLES'] = '1'
         env['LD_LIBRARY_PATH'] = [
             # no, this will cause a failure at runtime if LD_LIBRARY_PATH is unset (or empty!)
             # Property('LD_LIBRARY_PATH'),
-            Transform(os.path.join, hexagon_remote_bin, 'host'),
+            hexagon_remote_bin,
             Interpolate('%(prop:HL_HEXAGON_TOOLS)s/lib/iss'),
         ]
         env['HEXAGON_SDK_ROOT'] = Interpolate('%(prop:HL_HEXAGON_TOOLS)s/../../../..')