allow diverging nogil declaration, but only when assigning a nogil function to a gil pointer

Cython/Compiler/PyrexTypes.py

@@ -695,7 +695,7 @@ class CFuncType(CType):
             return 0
         if not self.same_calling_convention_as(other_type):
             return 0
-        if self.nogil != other_type.nogil:
+        if self.nogil and not other_type.nogil:
             return 0
         return 1
 

tests/errors/nogilfunctype.pyx

 cdef extern from *:
-    cdef void f() nogil
-    cdef void (*fp)()
+    cdef void f()
+    cdef void (*fp)() nogil
+
+    cdef void g() nogil
+    cdef void (*gp)()
+
+gp = g
 
 fp = f
 
 _ERRORS = u"""
-5:6: Cannot assign type 'void (void) nogil' to 'void (*)(void)'
+10:6: Cannot assign type 'void (void)' to 'void (*)(void) nogil'
 """