Document the ieee754-h module better

[Bruno Haible]

The ieee754-h module was listed under "Undocumented modules".
This patch fixes it.


2024-12-27  Bruno Haible  <bruno@clisp.org>

        Document the ieee754-h module better.
        * doc/glibc-headers/ieee754.texi: Mention the module ieee754-h. Give an
        example of a platform without IEEE floating-point numbers.

diff --git a/doc/glibc-headers/ieee754.texi b/doc/glibc-headers/ieee754.texi
index 4bc0869a89..35ef4f930c 100644
--- a/doc/glibc-headers/ieee754.texi
+++ b/doc/glibc-headers/ieee754.texi
@@ -4,7 +4,8 @@
 Defines the types @code{union ieee754_float}, @code{union ieee754_double},
 @code{union ieee854_long_double}.
 
-Gnulib module: ---
+Gnulib module: ieee754-h
+@mindex ieee754-h
 
 Portability problems fixed by Gnulib:
 @itemize
@@ -21,5 +22,5 @@
 
 @item
 The substitute for this header file returns nonsense on (now-quite-rare)
-platforms that do not use IEEE floating point.
+platforms that do not use IEEE floating point, such as Linux/m68k.
 @end itemize