--- work/siputils.py.orig	2017-09-04 07:49:58.370772959 +0000
+++ work/siputils.py	2017-09-04 07:50:07.367771132 +0000
@@ -1157,9 +1157,11 @@
         if self._deployment_target:
             mfile.write("export MACOSX_DEPLOYMENT_TARGET = %s\n" % self._deployment_target)
 
-        mfile.write("CC = %s\n" % self.required_string("CC"))
-        mfile.write("CXX = %s\n" % self.required_string("CXX"))
-        mfile.write("LINK = %s\n" % self.required_string("LINK"))
+        # Really we want to be testing for nmake here instead since it does not grok '?='
+        maybe_env = '=' if sys.platform == "win32" else '?='
+        mfile.write("CC %s %s\n" % (maybe_env, self.required_string("CC")))
+        mfile.write("CXX %s %s\n" % (maybe_env, self.required_string("CXX")))
+        mfile.write("LINK %s %s\n" % (maybe_env, self.required_string("LINK")))
 
         cppflags = []