Pic device specific header and c source files are automatically generated
from MPLAB include files, which are published by Microchip with a
special requirement that they are only to be used with authentic Microchip
devices. This requirement prevents to publish generated header and
c source files under the GPL compatible license, so they are located
in the non-free directory (see section 2.3).
In order to include them in include and library search paths, the
—use-non-free
command line option should be defined.
NOTE: the compiled code, which use non-free pic device specific libraries,
is not GPL compatible!