Make libinput.h safe to be included from C++

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>

src/libinput.h

@@ -23,6 +23,10 @@
 #ifndef LIBINPUT_H
 #define LIBINPUT_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <stdlib.h>
 #include <stdint.h>
 #include <libudev.h>
@@ -1211,4 +1215,8 @@ int
 libinput_device_has_capability(struct libinput_device *device,
 			       enum libinput_device_capability capability);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* LIBINPUT_H */