Fix MSVC: Add an explicit warning to modules that use the "array.array"...

Fix MSVC: Add an explicit warning to modules that use the "array.array" internals and try to compile in PyPy.
Closes https://github.com/cython/cython/issues/3448

Cython/Includes/cpython/array.pxd

@@ -50,8 +50,12 @@
 cdef extern from *:
     """
     #if CYTHON_COMPILING_IN_PYPY
+    #ifdef _MSC_VER
+    #pragma message ("This module uses CPython specific internals of 'array.array', which are not available in PyPy.")
+    #else
     #warning This module uses CPython specific internals of 'array.array', which are not available in PyPy.
     #endif
+    #endif
     """
 
 from libc.string cimport memset, memcpy