From ctag 5.8 help file :
FILES
/ctags.cnf (on MSDOS, MSWindows only)
/etc/ctags.conf
/usr/local/etc/ctags.conf
$HOME/.ctags
$HOME/ctags.cnf (on MSDOS, MSWindows only)
.ctags
ctags.cnf (on MSDOS, MSWindows only)
If any of these configuration files exist, each will be expected to contain
a set of default options which are read in the order listed when ctags starts,
but before the CTAGS environment variable is read or any command line options
are read. (...)
So creating a ctags.conf
in your C:/users/USER/
directory should work.
You can run ctags --list-languages
to display the list of all supported languages and check that VHDL
is indeed in the list.