stdlib: strtod: Hide internal symbol __dtoa

Change-Id: Iaaec7ea4d04c859fe98ad3331fd71e7d000c826b
diff --git a/libc/stdlib/strtod.c b/libc/stdlib/strtod.c
index 9d599b0..2851506 100644
--- a/libc/stdlib/strtod.c
+++ b/libc/stdlib/strtod.c
@@ -2062,7 +2062,7 @@
  *	   calculation.
  */
 
- char *
+__LIBC_HIDDEN__  char *
 __dtoa
 #ifdef KR_headers
 	(_d, mode, ndigits, decpt, sign, rve)