Remove redundant void from C++ sources (#1486)

diff --git a/src/hb-atomic.hh b/src/hb-atomic.hh
index 575d536..7df4fe9 100644
--- a/src/hb-atomic.hh
+++ b/src/hb-atomic.hh
@@ -104,7 +104,7 @@
 
 #include <windows.h>
 
-static inline void _hb_memory_barrier (void)
+static inline void _hb_memory_barrier ()
 {
 #if !defined(MemoryBarrier)
   /* MinGW has a convoluted history of supporting MemoryBarrier. */
@@ -269,10 +269,10 @@
 {
   void set_relaxed (int v_) { hb_atomic_int_impl_set_relaxed (&v, v_); }
   void set (int v_) { hb_atomic_int_impl_set (&v, v_); }
-  int get_relaxed (void) const { return hb_atomic_int_impl_get_relaxed (&v); }
-  int get (void) const { return hb_atomic_int_impl_get (&v); }
-  int inc (void) { return hb_atomic_int_impl_add (&v,  1); }
-  int dec (void) { return hb_atomic_int_impl_add (&v, -1); }
+  int get_relaxed () const { return hb_atomic_int_impl_get_relaxed (&v); }
+  int get () const { return hb_atomic_int_impl_get (&v); }
+  int inc () { return hb_atomic_int_impl_add (&v,  1); }
+  int dec () { return hb_atomic_int_impl_add (&v, -1); }
 
   int v;
 };
@@ -286,12 +286,12 @@
 
   void init (T* v_ = nullptr) { set_relaxed (v_); }
   void set_relaxed (T* v_) { hb_atomic_ptr_impl_set_relaxed (&v, v_); }
-  T *get_relaxed (void) const { return (T *) hb_atomic_ptr_impl_get_relaxed (&v); }
-  T *get (void) const { return (T *) hb_atomic_ptr_impl_get ((void **) &v); }
+  T *get_relaxed () const { return (T *) hb_atomic_ptr_impl_get_relaxed (&v); }
+  T *get () const { return (T *) hb_atomic_ptr_impl_get ((void **) &v); }
   bool cmpexch (const T *old, T *new_) const { return hb_atomic_ptr_impl_cmpexch ((void **) &v, (void *) old, (void *) new_); }
 
-  T * operator -> (void) const { return get (); }
-  template <typename C> operator C * (void) const { return get (); }
+  T * operator -> () const                    { return get (); }
+  template <typename C> operator C * () const { return get (); }
 
   T *v;
 };