Add GNU Make based build-system

[nto]

Replace the current build system with a GNU Make based system mostly compatible with existing configure usage and automake features, including out-of-tree builds, partial execution in subdirectories and test-suite support.

The following statistics show how much simpler and more efficient this new system is (times recorded on a ccache-enabled 96-core machine):

	autotools	Build.mk
files	122	44
loc	6129	3164
configure	9s	1s
build	29s	6s

Additionally, this new build system brings the following features:

• depends on GNU Make and pkg-config only
• maximum parallelization between subdirectories
• overview of modules dependencies using make config-deps
• automatic generation of pkg-config files
• json compilation database generation for clang tooling
• builtin support for code sanitizers
• progress counter using PROGRESS=1 or P=1
• time profiler to find bottlenecks for optimizing build duration

A small configure shell script is provided for compatibility with autotools but is not strictly needed. A full build can be achieved using makefiles only, using either on-the-fly config checks or using make configure beforehand, which enables caching of config checks.