[CMake] Installing systemd service files that point to my installed location

[Matthew Karas]

This is probably and XY problem but...

I'm trying to install a systemd file in my cmake.

The service file needs to point at the installed destination of my
build after I "make install".

I was trying to use  "CONFIGURE_FILE"

When I tried to do this - the variable is blank because the configure
file occurs during the cmake setup part - not the make install
DESTDIR=~/blah part.

Is there any way to configure files while I'm installing them, or to
configure a file as part of a post install script?

Thanks,
Matt