fix FTBS on non-udev target platforms (eg. FreeBSD)

On platforms that don't have libudev at all (eg. FreeBSD), the build
breaks. The only consumer, EvdevDeviceIsVirtual(), can live well with
just bailing out directly if libudev isn't present.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/driver/xf86-input-evdev/-/merge_requests/6>

configure.ac

@@ -45,7 +45,7 @@ XORG_DEFAULT_OPTIONS
 
 # Obtain compiler/linker options from server and required extensions
 PKG_CHECK_MODULES(XORG, [xorg-server >= 1.18] xproto [inputproto >= 2.1.99.3])
-PKG_CHECK_MODULES(UDEV, libudev)
+PKG_CHECK_MODULES(UDEV, libudev, [AC_DEFINE(HAVE_LIBUDEV, 1,[libudev support])])
 
 PKG_CHECK_MODULES(LIBEVDEV, [libevdev >= 0.4])
 PKG_CHECK_MODULES(MTDEV, mtdev)

src/evdev.c

@@ -39,7 +39,9 @@
 #include <X11/extensions/XI.h>
 
 #include <sys/stat.h>
+#ifdef HAVE_LIBUDEV
 #include <libudev.h>
+#endif
 #include <unistd.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -225,6 +227,7 @@ EvdevIsDuplicate(InputInfoPtr pInfo)
 static BOOL
 EvdevDeviceIsVirtual(const char* devicenode)
 {
+#ifdef HAVE_LIBUDEV
     struct udev *udev = NULL;
     struct udev_device *device = NULL;
     struct stat st;
@@ -255,6 +258,9 @@ out:
     udev_device_unref(device);
     udev_unref(udev);
     return rc;
+#else
+    return FALSE;
+#endif
 }