I can't get 'gtags' to process a .inc file as C file

Hi:

I am using gtags version 6.5.1 built with exuberant-ctags  that is in 
/bin/ctags on my fedora distribution (version 5.8 of exuberant-ctags)

I have several .inc files that I need to have processed as C language 
src files and tags created for them. I can't figure out how to do this. 
I have tried even to add ".inc" in langmap for "C" in gtags.conf file 
that I have copied as ~/.globalrc file.

Is there a simple way to do this? I tried to create a file w/ name of 
just my  .inc file, and tried:

gtags -f  flist --explain   and nothing  happens.  While "gtags 
--explain" goes to work on my source tree and explains what it is doing 
for each file.

Any hints welcome. My .inc file contains valid C source, just need them 
included in my gtags output.

Gautam