A small pile of Windows compiler-warning fixes.

These include an unused variable left over from the command-line
refactoring; an explicit referencing of the module handle for
sspicli.dll which we really do deliberately load and then don't
(directly) use; a missing pointer-type cast in the Windows handle
socket code; and two 32/64 bit integer size mismatches in the types of
functions I was importing from system API DLLs.

The last of those are a bit worrying, and suggest to me that after
going to all that trouble to add type-checking of those runtime
imports in commit 49fb598b0, I might have only checked the resulting
compiler output in a 32-bit build and not a 64-bit one. Oops!

windows/winmisc.c

@@ -106,6 +106,7 @@ char *get_username(void)
 	       sspicli.dll WITHOUT proper path sanitizing, so better
 	       load it properly before */
 	    HMODULE sspicli = load_system32_dll("sspicli.dll");
+            (void)sspicli; /* squash compiler warning about unused variable */
 	    GET_WINDOWS_FUNCTION(secur32, GetUserNameExA);
 	    tried_usernameex = TRUE;
 	}