[Buildroot] Extend and use the <pkg>_CONFIG_FIXUP infra

[Thomas Petazzoni]

Hello,

This patch series improves on the <pkg>_CONFIG_FIXUP work done by
Stefan Fröberg by:

 * Renaming the variable to <pkg>_CONFIG_SCRIPTS. I believe this is
   needed, because we will not only "fixup" those files, but also
   remove them from the target directory. Also, I don't think the
   variable name should indicate what will happen to these files. It
   should just indicate what those files are.

 * Extending the <pkg>_CONFIG_SCRIPTS handling to remove the config
   scripts from the TARGET_DIR, unless BR2_HAVE_DEVFILES is set (even
   though it is deprecated, it is still here).

 * Use <pkg>_CONFIG_SCRIPTS in a number of packages that were already
   fixing manually their <foo>-config script and for which the new
   infrastructure does exactly the same thing.

 * Use <pkg>_CONFIG_SCRIPTS in a number of packages that were doing a
   bit more than the infrastructure: fixing the includedir and libdir
   fields. A manual inspection of each of those packages shows that by
   default, the includedir and libdir are described relatively to
   prefix and exec_prefix, so fixing up those is sufficient, and this
   is what the infrastructure does.

 * Use <pkg>_CONFIG_SCRIPTS to fix up gpg-error-config installed by
   the libgpg-error package. This is done separately from the previous
   patch, because libgpg-error was not previously doing any fix up of
   its gpg-error-config script.

Best regards,

Thomas