Use a headerfile for cfuncs.c, otherwise this test code will fail to build on Windows

See https://mail.python.org/pipermail/cython-devel/2016-April/004777.html

Cython/Debugger/Tests/TestLibCython.py

@@ -94,6 +94,8 @@ class DebuggerTestCase(unittest.TestCase):
 
             shutil.copy(codefile, self.destfile)
             shutil.copy(cfuncs_file, self.cfuncs_destfile + '.c')
+            shutil.copy(cfuncs_file.replace('.c', '.h'),
+                        self.cfuncs_destfile + '.h')
 
             compiler = ccompiler.new_compiler()
             compiler.compile(['cfuncs.c'], debug=True, extra_postargs=['-fPIC'])

Cython/Debugger/Tests/cfuncs.h

+void some_c_function(void);

Cython/Debugger/Tests/codefile

 cdef extern from "stdio.h":
     int puts(char *s)
 
-cdef extern:
+cdef extern from "cfuncs.h":
     void some_c_function()
 
 import os