configure: improve usbfs check

The current check to test if usbfs support should be compiled or not
solely relies on the presence of <linux/usbdevice_fs.h>, without
actually checking that all definition used by Qemu are provided by
this header file.

With sufficiently old kernel headers, <linux/usbdevice_fs.h> may be
present, but some of the definitions needed by Qemu may not be
available.

This commit improves the check by building a small program that
actually tests whether the necessary definitions are available.

In addition, it fixes a bug where have_usbfs was set to "yes"
regardless of the result of the test.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190213211827.20300-1-thomas.petazzoni@bootlin.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

configure

@@ -4262,10 +4262,25 @@ fi
 # check for usbfs
 have_usbfs=no
 if test "$linux_user" = "yes"; then
-  if check_include linux/usbdevice_fs.h; then
+  cat > $TMPC << EOF
+#include <linux/usbdevice_fs.h>
+
+#ifndef USBDEVFS_GET_CAPABILITIES
+#error "USBDEVFS_GET_CAPABILITIES undefined"
+#endif
+
+#ifndef USBDEVFS_DISCONNECT_CLAIM
+#error "USBDEVFS_DISCONNECT_CLAIM undefined"
+#endif
+
+int main(void)
+{
+    return 0;
+}
+EOF
+  if compile_prog "" ""; then
     have_usbfs=yes
   fi
-  have_usbfs=yes
 fi
 
 # check for fallocate