--- SConstruct.orig	2018-12-22 14:00:12 UTC
+++ SConstruct
@@ -28,15 +28,18 @@ clang = int(ARGUMENTS.get("clang", 0))
 cycles = int(ARGUMENTS.get('cycles', 1))
 sound = False
 
-if os.environ.get('CC') == 'clang': clang = 1
+import subprocess
+if 'clang' in subprocess.check_output([os.environ.get('CC', 'cc'), '-v'],
+                                      stderr=subprocess.STDOUT):
+    clang = 1
+print 'clang', clang
 if profile: debug = 0
 
-env = Environment(ENV = os.environ)
+
+env = Environment(ENV = os.environ, CC = os.environ.get('CC', 'cc'),
+                  CXX = os.environ.get('CXX', 'c++'))
 conf = env.Configure()
 
-if clang:
-    env.Replace(CC='clang', CXX='clang++')
-
 # Asan & Ubsan (need to come first).
 # Cycles doesn't like libasan with clang, so we only use it on
 # C code with clang.
@@ -145,7 +148,7 @@ if cycles:
     sources += glob.glob('ext_src/cycles/src/subd/*.cpp')
 
     env.Append(CPPPATH=['ext_src/cycles/src'])
-    env.Append(CPPPATH=['ext_src/cycles/third_party/atomic'])
+    env.Prepend(CPPPATH=['ext_src/cycles/third_party/atomic'])
     env.Append(CPPFLAGS=[
         '-DCYCLES_STD_UNORDERED_MAP',
         '-DCCL_NAMESPACE_BEGIN=namespace ccl {',