Exclude 'const' globals from star-importing since they can't get assigned anyway.

Closes #2621.

CHANGES.rst

@@ -105,6 +105,10 @@ Bugs fixed
 * Generator expressions and lambdas failed to compile in ``@cfunc`` functions.
   (Github issue #459)
 
+* Global names with ``const`` types were not excluded from star-import assignments
+  which could lead to invalid C code.
+  (Github issue #2621)
+
 * Several internal function signatures were fixed that lead to warnings in gcc-8.
   (Github issue #2363)
 

Cython/Compiler/ModuleNode.py

@@ -2238,7 +2238,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         code.putln("if (0);")  # so the first one can be "else if"
         msvc_count = 0
         for name, entry in sorted(env.entries.items()):
-            if entry.is_cglobal and entry.used:
+            if entry.is_cglobal and entry.used and not entry.type.is_const:
                 msvc_count += 1
                 if msvc_count % 100 == 0:
                     code.putln("#ifdef _MSC_VER")