os_support: fix misleading comments

cherry-picked from speexdsp 86779a06f6500d041573d6252d4971d3bfcb4b18

libspeex/os_support.h

@@ -90,18 +90,18 @@ static inline void speex_free_scratch (void *ptr)
 }
 #endif
 
-/** Copy n bytes of memory from src to dst. The 0* term provides compile-time type checking  */
+/** Copy n elements from src to dst. The 0* term provides compile-time type checking  */
 #ifndef OVERRIDE_SPEEX_COPY
 #define SPEEX_COPY(dst, src, n) (memcpy((dst), (src), (n)*sizeof(*(dst)) + 0*((dst)-(src)) ))
 #endif
 
-/** Copy n bytes of memory from src to dst, allowing overlapping regions. The 0* term 
+/** Copy n elements from src to dst, allowing overlapping regions. The 0* term
     provides compile-time type checking */
 #ifndef OVERRIDE_SPEEX_MOVE
 #define SPEEX_MOVE(dst, src, n) (memmove((dst), (src), (n)*sizeof(*(dst)) + 0*((dst)-(src)) ))
 #endif
 
-/** Set n bytes of memory to value of c, starting at address s */
+/** For n elements worth of memory, set every byte to the value of c, starting at address dst */
 #ifndef OVERRIDE_SPEEX_MEMSET
 #define SPEEX_MEMSET(dst, c, n) (memset((dst), (c), (n)*sizeof(*(dst))))
 #endif