The standard is 9 years old now, it is well supported in all mayor compilers.
In fact, features of the 'new' standard are already used in RIOT (std_atomic).
Let's make it the default and adapt the Makefiles accordingly.
Prepare for handling pkg state with files. So it requires having the
path defined before declaring targets. In addition, it cleans up the
old git-download target.
export COMP by using the environment insteal of through the shell to
prevnet issues with `\"` being defined when keeping macros in CFLAGS.
Another solution was to use COMP='...' but could there could still have
issues with single quotes in CFLAGS.
relic does not build with cmake < 3.6.0. This checks for a minimal version
instead of failing to compile.
cmake version 3.5.2 is not >= to minimal required 3.6.0
Makefile:25: recipe for target '..cmake_version_supported' failed
