timegm: Document under ISO C and POSIX substitutes

[Bruno Haible]

Now that ISO C 23 has added the 'timegm' function, it needs to be documented
in a different section of the Gnulib manual.


2023-03-16  Bruno Haible  <bruno@clisp.org>

        timegm: Document under ISO C and POSIX substitutes.
        * doc/posix-functions/timegm.texi: Renamed from 
doc/glibc-functions/timegm.texi.
        * doc/gnulib.texi (Function Substitutes): Include timegm.texi here...
        (Glibc time.h): ... not here.

diff --git a/doc/gnulib.texi b/doc/gnulib.texi
index 28d8c20d8c..12766b2d96 100644
--- a/doc/gnulib.texi
+++ b/doc/gnulib.texi
@@ -2334,6 +2334,7 @@
 * thrd_sleep::
 * thrd_yield::
 * time::
+* timegm::
 * timer_create::
 * timer_delete::
 * timer_getoverrun::
@@ -3627,6 +3628,7 @@
 @include posix-functions/thrd_sleep.texi
 @include posix-functions/thrd_yield.texi
 @include posix-functions/time.texi
+@include posix-functions/timegm.texi
 @include posix-functions/timer_create.texi
 @include posix-functions/timer_delete.texi
 @include posix-functions/timer_getoverrun.texi
@@ -6619,7 +6621,6 @@
 * getdate_r::
 * stime::
 * strptime_l::
-* timegm::
 * timelocal::
 * timespec_get::
 @end menu
@@ -6629,7 +6630,6 @@
 @include glibc-functions/getdate_r.texi
 @include glibc-functions/stime.texi
 @include glibc-functions/strptime_l.texi
-@include glibc-functions/timegm.texi
 @include glibc-functions/timelocal.texi
 @include glibc-functions/timespec_get.texi
 
diff --git a/doc/glibc-functions/timegm.texi b/doc/posix-functions/timegm.texi
similarity index 95%
rename from doc/glibc-functions/timegm.texi
rename to doc/posix-functions/timegm.texi
index aeae4c97fa..9087d949a0 100644
--- a/doc/glibc-functions/timegm.texi
+++ b/doc/posix-functions/timegm.texi
@@ -1,5 +1,5 @@
 @node timegm
-@subsection @code{timegm}
+@section @code{timegm}
 @findex timegm
 
 Documentation: