[CMake] Programmatically-generated dependencies

[ax487]

Hello all,

I am mainly asking having glib-compile-resources in mind. This little
program translates files into C source code to be used with the
gresource system. It works in the following way: You have a file.xml
describing the resources:

<?xml version="1.0" encoding="UTF-8"?>
<gresources>
<gresource prefix="/some/prefix">

<file>some_file.txt</file>
</gresource>
</gresources>

To generate the source you use `glib-compile-resources --generate-source
--target=output.c file.xml`. Clearly the generated output.c depends on
file.xml. But it also depends on some_file.txt. It is possible to get a
list of dependencies using `glib-compile-resources
--generate-dependencies file.xml` which will output

some_file.txt

The situation is similar to the case of auto-generated header
dependencies for C/C++ source code using the "-MM" option of gcc.
I saw the following version on github:

https://github.com/bgK/vba-ttb/blob/master/cmake/GResource.cmake

which does not correctly detect dependencies, but nothing apart from
that. But since the process works with C/C++ source code I figured there
is no reason why it shouldn't also work in this case. Could anyone give
me some pointers on how to get this to work?

ax487