The version of mkmakefile which has been used in barebox until now dates
back to commit fd5f0cd from the Linux
kernel git history (Tue May 2 12:33:20 2006 +0200).
This patch effectively includes all changes from the aforementioned
commit to the latest stable version of the Linux kernel:

git log --pretty=oneline --abbrev-commit fd5f0cd..v4.10 scripts/mkmakefile
06ed5c2 kbuild: Make scripts executable
9319f45 kbuild: support simultaneous "make %config" and "make all"
0ff3577 kbuild: silence generated makefile message
3c955b4 fixes for using make 3.82
d230124 kbuild: teach mkmakfile to be silent
1d3b3bf kbuild: scripts/mkmakefile: dynamic determination of output directory
971edcf kbuild: re-enable Makefile generation in a new O=... directory
18c32da kbuild: fix building with O=.. options
0b35786 kbuild: call make once for all targets when O=.. is used

In particular, the list of changes includes a fix for the following
Make warning:

  Makefile:18: *** mixed implicit and normal rules: deprecated syntax

GNU Make 3.82 raises an error instead of a warning and aborts the
make process. GNU Make 3.82 is still used today by distributions
like Red Hat Enterprise Linux 7.3.

Signed-off-by: Dennis Menschel <menschel-d@posteo.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>