compat: mark unused parameters in win32/mingw functions

The compat/ directory contains many stub functions, wrappers, and so on
that have to conform to a specific interface, but don't necessarily need
to use all of their parameters. Let's mark them to avoid complaints from
-Wunused-parameter.

This was done mostly via guess-and-check with the Windows build in
GitHub CI. I also confirmed that the win+VS build is similarly happy.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/winansi.c

@@ -340,7 +340,7 @@ enum {
 	TEXT = 0, ESCAPE = 033, BRACKET = '['
 };
 
-static DWORD WINAPI console_thread(LPVOID unused)
+static DWORD WINAPI console_thread(LPVOID data UNUSED)
 {
 	unsigned char buffer[BUFFER_SIZE];
 	DWORD bytes;