Add missing @section.

From-SVN: r24057

gcc/extend.texi

@@ -794,6 +794,8 @@ A future version of GDB will know how to recognize such pairs and treat
 them as a single variable with a complex type.
 
 @node Hex Floats
+@section Hex Floats
+@cindex hex floats
 GNU CC recognizes floating-point numbers written not only in the usual
 decimal notation, such as @code{1.55e1}, but also numbers such as
 @code{0x1.fp3} written in hexadecimal format.  In that format the