aarch64: use MACH-O const data asm directive in const macro

libavutil/aarch64/asm.S

@@ -57,7 +57,11 @@ FUNC    .func   \name
 ELF     .size   \name, . - \name
         .purgem endconst
     .endm
+#ifndef __MACH__
         .section        .rodata
+#else
+        .const_data
+#endif
         .align          \align
 \name:
 .endm