libc: don't export unnecessary symbols

Symbols associated with the internal implementation of memcpy
like routines should be private.

Change-Id: I2b1d1f59006395c29d518c153928437b08f93d16
diff --git a/libc/arch-arm/cortex-a9/bionic/memset.S b/libc/arch-arm/cortex-a9/bionic/memset.S
index 87d2c08..f6be66a 100644
--- a/libc/arch-arm/cortex-a9/bionic/memset.S
+++ b/libc/arch-arm/cortex-a9/bionic/memset.S
@@ -119,7 +119,7 @@
         .cfi_endproc
 END(memset)
 
-ENTRY(__memset_large_copy)
+ENTRY_PRIVATE(__memset_large_copy)
         .cfi_startproc
 
         /* compute the offset to align the destination