How to force libtool to use CXX mode?

I have expended quite a few days already (over a 6 month span) with 
attempting to convince Automake to force libtool to link using the C++ 
compiler.  I tried optionally adding an empty C++ source file to the 
target build but this does not work because then Automake always assumes 
C++ linkage, even if no C++ source files were included. I previously 
encountered a libtool-related bug where it determines that the C 
compiler needs -lm, but the C++ compiler does not, stripping the -lm and 
resulting in a failed link.

Today I read this Automake manual page:

https://www.gnu.org/software/automake/manual/html_node/Libtool-Flags.html

and so I used the program_LIBTOOLFLAGS or library_LIBTOOLFLAGS to add 
--tag=CXX to the options.  I thought that this must be working.

I found that it is not working as desired.  I end up with this bad case 
for compiling C code (did not want to have the --tag=CXX!)

     /bin/bash ./libtool  --tag=CC --tag=CXX  --mode=compile clang ...

and this command to link the C code using the C++ compiler (should be 
clang++!)

     /bin/bash ./libtool  --tag=CC --tag=CXX  --mode=link clang

Libtool misreports the tag it is using so it reports CCLD when the tag 
is presumably overridden by CXX.

The end result fails.

Is there a way to solve this problem beyond replicating many modified 
Makefile.in hunks into Makefile.am?

I am faced with backing out my attempt for yet another time. :-(

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