Portable method to change sysconfdir

[Stephen Torri]

I am looking for a portable method that will allow me to change the
location of files installed into the sysconfir ($prefix/etc). Right now
my Makefile.am contains:

dist_sysconf_DATA = \
        db_config.xml \
        file_config.xml \
        memory_config.xml

I want to install them to a named sub-directory in $prefix/etc. Also I
would like to have a entry made into config.h giving this location as
well or a flag used by the preprocessor. This way the program knows
where the default directory is to start looking for the configuration
files.

Stephen