.la file dependency_libs dropping sole -lm dependency

I am encountering an issue when building a static build of 
GraphicsMagick in that although -lm is supplied to libtool while 
linking the static library, the associated .la file is missing -lm in 
dependency_libs.  If several more libraries are specified (also 
including -lm) then they all seem to be included in dependency_libs. 
The linkage is using --tag=CXX because there are some modules compiled 
with C++.

Programs which depend on the library fail to link due to missing the 
symbols from '-lm'.

The libtool used reports itself as

   % /usr/local/bin/libtool --version
   libtool (GNU libtool) 2.4.7
   Written by Gordon Matzigkeit, 1996

   Copyright (C) 2014 Free Software Foundation, Inc.

which I think is confusing since the tarball date is 2022-03-17 and 
the copyright at the top of libtool.m4 is up to 2022 although several 
lines down where the copyright message comes from, I see "Copyright 
(C) 2014 Free Software Foundation, Inc.".

The OS used is Ubuntu 20.04 LTS.

My expectation is that the .la file in the build tree will remember 
which compiler/language needs to be used for linking, and remember the 
library dependencies, so that dependent libraries and programs which 
depend on the library do not need to.

In magick/libGraphicsMagick.la, I see:

   # Libraries that this one depends upon.
   dependency_libs=' -L/usr/local/lib'

rather than this:

   # Libraries that this one depends upon.
   dependency_libs=' -L/usr/local/lib' -lm

As a result, linking fails when programs which depend on this library 
attempt to link with it using libtool in the same build.

The linking request looks somewhat like (abbreviated for clarity):

bin/bash ./libtool  --tag=CXX --mode=link g++-10 -no-undefined 
-export-symbols-regex ".*"  -version-info 27:4:24 -L/usr/local/lib 
-Wl,-rpath,/usr/local/lib -o magick/libGraphicsMagick.la -rpath 
/usr/local/lib [ list of .lo files ] -lm

An I misunderstanding something, or is this a bug in libtool?  What am 
I missing in order for this to work?

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt