Add C23's memset_explicit().

https://open-std.org/jtc1/sc22/wg14/www/docs/n2897.htm

Test: treehugger
Change-Id: Ia0cfc72bdf3c22eda6a4fc9adaa4c0ca0ff9a7c8
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 79f331a..0f41878 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1580,6 +1580,7 @@
   global:
     close_range;
     copy_file_range;
+    memset_explicit;
 } LIBC_T;
 
 LIBC_PRIVATE {