Make sure we include <windows.h> to get HANDLE declared.

Change-Id: I8cba1120f4667864eadeebd48bcdced3a2b71f4c
Reviewed-on: https://code.wireshark.org/review/8867
Reviewed-by: Guy Harris <guy@alum.mit.edu>

wsutil/process.h

@@ -30,6 +30,8 @@ extern "C" {
 #endif /* __cplusplus */
 
 #ifdef _WIN32
+#include <windows.h>
+
 typedef HANDLE ws_process_id; /* on Windows, a process ID is a HANDLE */
 #else
 typedef pid_t ws_process_id;  /* on UN\*X, a process ID is a pid_t */