Always define WIN32_LEAN_AND_MEAN before <windows.h>

Recently, mingw-w64 has got updated <msxml.h> from Wine which is included
indirectly by <windows.h> if `WIN32_LEAN_AND_MEAN` is not defined. The
`IXMLDOMDocument` class has a member function named `abort()`, which gets
affected by our `abort()` macro in "system.h".

`WIN32_LEAN_AND_MEAN` should, nevertheless, always be defined. This
can exclude 'APIs such as Cryptography, DDE, RPC, Shell, and Windows
Sockets' [1], and speed up compilation of these files a bit.

[1] https://learn.microsoft.com/en-us/windows/win32/winprog/using-the-windows-headers

(cherry picked from commit 902c755)

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: lhmouse

libgo/misc/cgo/test/callback_c.c

@@ -32,6 +32,7 @@ IntoC(void)
 }
 
 #ifdef WIN32
+#define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 long long
 mysleep(int seconds) {