src: make and use a config.h file
Not every system is the same.
Automatically create a config.h file that contains
"interesting" information about a system that cannot
be determined at compile time via predefined macros.
Provide this file via a CONFIG_H macro to interested
source files that can then `#include CONFIG_H` when
it's defined.
Currently only the framework is provided. In other
words, the config.h file is created but is always
empty and the proper CONFIG_H macro definition is
passed on to interested source files.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>