cffi: respect CC environment variable for defining compiler

Closes #103.

NEWS.rst

@@ -89,6 +89,8 @@ Backwards Compatibility Notes
 Changes
 -------
 
+* The ``make_cffi.py`` script should now respect the ``CC`` environment
+  variable for locating the compiler. (#103)
 * CI now properly uses the ``cffi`` backend when running all tests.
 * ``train_dictionary()`` has been rewritten to use the ``fastcover`` APIs
   and to consistently call ``ZDICT_optimizeTrainFromBuffer_fastCover()``

make_cffi.py

@@ -84,12 +84,13 @@
 # Distutils doesn't set compiler.preprocessor, so invoke the preprocessor
 # manually.
 if compiler.compiler_type == "unix":
-    args = list(compiler.executables["compiler"])
+    # Using .compiler respects the CC environment variable.
+    args = [compiler.compiler[0]]
     args.extend(
         ["-E", "-DZSTD_STATIC_LINKING_ONLY", "-DZDICT_STATIC_LINKING_ONLY",]
     )
 elif compiler.compiler_type == "msvc":
-    args = [compiler.cc]
+    args = [compiler.compiler[0]]
     args.extend(
         ["/EP", "/DZSTD_STATIC_LINKING_ONLY", "/DZDICT_STATIC_LINKING_ONLY",]
     )