doc: Fix placement of memset_explicit node

[Bruno Haible]

In the HTML-formatted Gnulib documentation, the node for
memset_explicit appears as a child node of the one for memset.
This is obviously not intended, since memset_explicit and memset
are separate functions. This patch fixes it.


2023-03-28  Bruno Haible  <bruno@clisp.org>

        doc: Fix placement of memset_explicit node.
        * doc/posix-functions/memset_explicit.texi: Define a section, not a
        subsection.

diff --git a/doc/posix-functions/memset_explicit.texi 
b/doc/posix-functions/memset_explicit.texi
index 528cee4e2b..2bfe82932a 100644
--- a/doc/posix-functions/memset_explicit.texi
+++ b/doc/posix-functions/memset_explicit.texi
@@ -1,5 +1,5 @@
 @node memset_explicit
-@subsection @code{memset_explicit}
+@section @code{memset_explicit}
 @findex memset_explicit
 
 Documentation: