Change two occurances of "behavour" to "behaviour".

Signed-off-by: Linus Nilsson <lajnold@acc.umu.se>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

The check introduced in commit:
4f1127e204377cbd2a56d112d323466f668e8334 "kbuild: fix
infinite make recursion"

caused certain external modules not to build and
also caused 'make targz-pkg' to fail.
This is a minimal fix so we revert to previous
behaviour - but we do not overwrite the Makefile
in the top-level directory.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Jay Cliburn <jacliburn@bellsouth.net>
Cc: Jay Cliburn <jacliburn@bellsouth.net>

Jan Altenberg <jan.altenberg@linutronix.de> reported that
building with redirected input like this failed:
make O=dir oldconfig bzImage < /dev/null

The problem were caused by a make silentoldconfig being
run before oldconfig and with a non-recent .config the build
failed because silentoldconfig requires non-redirected stdin.

Silentoldconfig was run as a side-effect of having the
top-level Makefile re-made by make.
Introducing an empty rule for the top-level Makefile
(and Kbuild.include) fixed the issue.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>