libvisual/lv_mem.c: Address warnings -Wreturn-type and -Wunused-function

Symptom was:
> ../../libvisual-0.4.2/libvisual/lv_mem.c: In function 'mem_copy_altivec':
> ../../libvisual-0.4.2/libvisual/lv_mem.c:379:1: error: no return statement in function returning non-void [-Werror=return-type]
>   379 | }
>       | ^
> ../../libvisual-0.4.2/libvisual/lv_mem.c: In function 'mem_set8_altivec':
> ../../libvisual-0.4.2/libvisual/lv_mem.c:529:1: error: no return statement in function returning non-void [-Werror=return-type]
>   529 | }
>       | ^
> ../../libvisual-0.4.2/libvisual/lv_mem.c: In function 'mem_set16_altivec':
> ../../libvisual-0.4.2/libvisual/lv_mem.c:673:1: error: no return statement in function returning non-void [-Werror=return-type]
>   673 | }
>       | ^
> ../../libvisual-0.4.2/libvisual/lv_mem.c: In function 'mem_set32_altivec':
> ../../libvisual-0.4.2/libvisual/lv_mem.c:784:1: error: no return statement in function returning non-void [-Werror=return-type]
>   784 | }
>       | ^
> ../../libvisual-0.4.2/libvisual/lv_mem.c: At top level:
> ../../libvisual-0.4.2/libvisual/lv_mem.c:781:14: error: 'mem_set32_altivec' defined but not used [-Werror=unused-function]
>   781 | static void *mem_set32_altivec (void *dest, int c, visual_size_t n)
>       |              ^~~~~~~~~~~~~~~~~
> ../../libvisual-0.4.2/libvisual/lv_mem.c:670:14: error: 'mem_set16_altivec' defined but not used [-Werror=unused-function]
>   670 | static void *mem_set16_altivec (void *dest, int c, visual_size_t n)
>       |              ^~~~~~~~~~~~~~~~~
> ../../libvisual-0.4.2/libvisual/lv_mem.c:526:14: error: 'mem_set8_altivec' defined but not used [-Werror=unused-function]
>   526 | static void *mem_set8_altivec (void *dest, int c, visual_size_t n)
>       |              ^~~~~~~~~~~~~~~~
> ../../libvisual-0.4.2/libvisual/lv_mem.c:376:14: error: 'mem_copy_altivec' defined but not used [-Werror=unused-function]
>   376 | static void *mem_copy_altivec (void *dest, const void *src, visual_size_t n)
>       |              ^~~~~~~~~~~~~~~~

Author: hartwork

libvisual/libvisual/lv_mem.c

@@ -41,22 +41,18 @@ static void *mem_copy_c (void *dest, const void *src, visual_size_t n);
 static void *mem_copy_mmx (void *dest, const void *src, visual_size_t n);
 static void *mem_copy_mmx2 (void *dest, const void *src, visual_size_t n);
 static void *mem_copy_3dnow (void *dest, const void *src, visual_size_t n);
-static void *mem_copy_altivec (void *dest, const void *src, visual_size_t n);
 
 static void *mem_set8_c (void *dest, int c, visual_size_t n);
 static void *mem_set8_mmx (void *dest, int c, visual_size_t n);
 static void *mem_set8_mmx2 (void *dest, int c, visual_size_t n);
-static void *mem_set8_altivec (void *dest, int c, visual_size_t n);
 
 static void *mem_set16_c (void *dest, int c, visual_size_t n);
 static void *mem_set16_mmx (void *dest, int c, visual_size_t n);
 static void *mem_set16_mmx2 (void *dest, int c, visual_size_t n);
-static void *mem_set16_altivec (void *dest, int c, visual_size_t n);
 
 static void *mem_set32_c (void *dest, int c, visual_size_t n);
 static void *mem_set32_mmx (void *dest, int c, visual_size_t n);
 static void *mem_set32_mmx2 (void *dest, int c, visual_size_t n);
-static void *mem_set32_altivec (void *dest, int c, visual_size_t n);
 
 /* Optimal performance functions set by visual_mem_initialize(). */
 VisMemCopyFunc visual_mem_copy = mem_copy_c;
@@ -373,11 +369,6 @@ static void *mem_copy_3dnow (void *dest, const void *src, visual_size_t n)
 	return dest;
 }
 
-static void *mem_copy_altivec (void *dest, const void *src, visual_size_t n)
-{
-
-}
-
 /* Memset functions, 1 byte memset */
 static void *mem_set8_c (void *dest, int c, visual_size_t n)
 {
@@ -523,11 +514,6 @@ static void *mem_set8_mmx2 (void *dest, int c, visual_size_t n)
 	return dest;
 }
 
-static void *mem_set8_altivec (void *dest, int c, visual_size_t n)
-{
-
-}
-
 /* Memset functions, 2 byte memset */
 static void *mem_set16_c (void *dest, int c, visual_size_t n)
 {
@@ -667,11 +653,6 @@ static void *mem_set16_mmx2 (void *dest, int c, visual_size_t n)
 	return dest;
 }
 
-static void *mem_set16_altivec (void *dest, int c, visual_size_t n)
-{
-
-}
-
 /* Memset functions, 4 byte memset */
 static void *mem_set32_c (void *dest, int c, visual_size_t n)
 {
@@ -778,11 +759,6 @@ static void *mem_set32_mmx2 (void *dest, int c, visual_size_t n)
 	return dest;
 }
 
-static void *mem_set32_altivec (void *dest, int c, visual_size_t n)
-{
-
-}
-
 /**
  * @}
  */