wxx: Fix compilation of host-libusb.c

libusb.h uses the WINAPI calling convention for all function callbacks.

Cross compilation with Mingw-w64 on Cygwin fails when this calling
convention is missing.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1469775331-7468-1-git-send-email-sw@weilnetz.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/host-libusb.c

@@ -359,7 +359,7 @@ static USBHostRequest *usb_host_req_find(USBHostDevice *s, USBPacket *p)
     return NULL;
 }
 
-static void usb_host_req_complete_ctrl(struct libusb_transfer *xfer)
+static void LIBUSB_CALL usb_host_req_complete_ctrl(struct libusb_transfer *xfer)
 {
     USBHostRequest *r = xfer->user_data;
     USBHostDevice  *s = r->host;
@@ -392,7 +392,7 @@ out:
     }
 }
 
-static void usb_host_req_complete_data(struct libusb_transfer *xfer)
+static void LIBUSB_CALL usb_host_req_complete_data(struct libusb_transfer *xfer)
 {
     USBHostRequest *r = xfer->user_data;
     USBHostDevice  *s = r->host;
@@ -448,7 +448,8 @@ static void usb_host_req_abort(USBHostRequest *r)
 
 /* ------------------------------------------------------------------------ */
 
-static void usb_host_req_complete_iso(struct libusb_transfer *transfer)
+static void LIBUSB_CALL
+usb_host_req_complete_iso(struct libusb_transfer *transfer)
 {
     USBHostIsoXfer *xfer = transfer->user_data;