Xext/xf86bigfont: guard the Unix-only bits for mingw (Windows)

Building the extension on mingw (Windows, no SysV SHM → CONFIG_MITSHM off)
failed on two counts:

  - QueryVersion filled the reply's uid/gid via geteuid()/getegid(), which
    Windows has no equivalent for (implicit-declaration error). Those fields
    only matter for the CONFIG_MITSHM local-shm path (off on Windows), so
    guard them (`#if !defined(WIN32) || defined(__CYGWIN__)` — Cygwin does
    have them); on native Windows uid/gid stay 0.
  - stuff_flags is only consumed under CONFIG_MITSHM, so with SHM off it was
    set-but-unused (-Werror=unused-but-set-variable). Scope its declaration
    and assignment under CONFIG_MITSHM too, matching how pDesc is already
    handled in this function.

Verified the Linux (CONFIG_MITSHM, non-WIN32) path is unchanged and builds
clean; the Windows path is validated by the mingw32 CI lane.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

Xext/xf86bigfont/xf86bigfont.c

@@ -277,8 +277,10 @@ ProcXF86BigfontQueryVersion(ClientPtr client)
     xXF86BigfontQueryVersionReply reply = {
         .majorVersion = SERVER_XF86BIGFONT_MAJOR_VERSION,
         .minorVersion = SERVER_XF86BIGFONT_MINOR_VERSION,
+#if !defined(WIN32) || defined(__CYGWIN__)
         .uid = geteuid(),
         .gid = getegid(),
+#endif
 #ifdef CONFIG_MITSHM
         .signature = signature,
         .capabilities = (client->local && !client->swapped)
@@ -329,7 +331,9 @@ ProcXF86BigfontQueryFont(ClientPtr client)
     X_REQUEST_FIELD_CARD32(id);
 
     FontPtr pFont;
+#ifdef CONFIG_MITSHM
     CARD32 stuff_flags;
+#endif
     xCharInfo *pmax;
     xCharInfo *pmin;
     int nCharInfos;
@@ -348,11 +352,15 @@ ProcXF86BigfontQueryFont(ClientPtr client)
     /* protocol version is decided based on request packet size */
     switch (client->req_len) {
     case 2:                    /* client with version 1.0 libX11 */
+#ifdef CONFIG_MITSHM
         stuff_flags = (client->local &&
                        !client->swapped ? XF86Bigfont_FLAGS_Shm : 0);
+#endif
         break;
     case 3:                    /* client with version 1.1 libX11 */
+#ifdef CONFIG_MITSHM
         stuff_flags = stuff->flags;
+#endif
         break;
     default:
         return BadLength;