gengetopt: new package

Add a host only package, which will be needed for janus-gateway.

[Thomas:
  - Improve commit log.
  - Remove target variant of the package, not needed as we don't do
    development on the target.
  - Remove Config.in.host option for the package, there is not really
    a need to select it from menuconfig, it's merely a build
    dependency for another package.
  - Fix format of hash file.
  - Fix format of comment header in .mk file.
  - Use BR2_GNU_MIRROR.
  - License is GPLv3+, not GPLv3.
  - Add 'LICENSE' to the license files, as it indicates that the
    license is GPLv3+.
  - Add an explanation about $(MAKE1) being used.]

Signed-off-by: Gregory Dymarek <gregd72002@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>