[3.12] pythongh-127906: Declare timeval struct in pytime.h on Windows (python#127908)

pythongh-127906: Declare timeval struct in pytime.h on Windows

Fix the following MSVC compiler warning:

    include\cpython\pytime.h(192): warning C4115: 'timeval':
    named type definition in parentheses

Author: vstinner

Include/cpython/pytime.h

@@ -53,7 +53,7 @@ functions and constants
 extern "C" {
 #endif
 
-#ifdef __clang__
+#if defined(__clang__) || defined(_MSC_VER)
 struct timeval;
 #endif