Use Clang 3.8 for Linux building.

xenia-build

@@ -503,8 +503,8 @@ class BaseBuildCommand(Command):
       print('ERROR: don\'t know how to build on this platform.')
     else:
       # TODO(benvanik): allow gcc?
-      os.environ['CXX'] = 'clang++'
-      os.environ['CC'] = 'clang'
+      os.environ['CXX'] = 'clang++-3.8'
+      os.environ['CC'] = 'clang-3.8'
       result = shell_call([
           'make',
           '-Cbuild/',