Allow conversion warnings in subsets of the code base. By allowing
this, we can improve the code base in parts, and see that those parts
do not regress in the future.

My approach to implement this is by adding support to our make system
to recognise and handle "variable packs". A "variable pack" is a list
of quoted variable "appendings". It will be picked up by
`NamedParamsMacroTemplate` and there recognised by the lack of an
assignment operator that is always used when sending variables to
macros today. To support sending lists of "variable appendings", the
appendings must quote assignment, spaces and quotes. This would be
cleanest to implement by hex or base64 encode the string. However,
this is extremely hard to do in make, and I prefer not calling the
likes of `od` or `base64` to make the code portable and fast.

With this infrastructure I implement a simple recursive utility to
find all files matching a pattern in a folder; I then transform that list
to variable assignments that will add compiler warnings for those files.

This approach is extremely flexible. I can for example combine many
calls to the `overrideFlags` macro with different source directories
and different patterns.

The macro will expand to something like (depending on compiler):
`module_file1.cpp_CXXFLAGS+=-Wconversion`
`module_file2.cpp_CXXFLAGS+=-Wconversion`

this can flexibly be combined with other flags to overlap:
`module_file2.cpp_CXXFLAGS+=$(SPACE)-Wotherflag`
`module_file3.cpp_CXXFLAGS+=$(SPACE)-Wotherflag`

(note the overlapping sets of flags `file1 -Wconversion`,
`file2 -Wconversion -Wotherflag`, `file3 -Wotherflag`)