Initial ability to swap compilers.

Fixes SPACK-16 and forces compiler script to build using compiler wrappers.

- works with gcc and clang on laptop.

bin/spack

@@ -41,7 +41,7 @@ sys.path.insert(0, SPACK_LIB_PATH)
 
 # If there is no working directory, use the spack prefix.
 try:
-    os.getcwd()
+    working_dir = os.getcwd()
 except OSError:
     os.chdir(SPACK_PREFIX)
 
@@ -79,6 +79,7 @@ args = parser.parse_args()
 # Set up environment based on args.
 spack.verbose = args.verbose
 spack.debug = args.debug
+spack.spack_working_dir = working_dir
 if args.mock:
     from spack.packages import PackageDB
     spack.db = PackageDB(spack.mock_packages_path)