kmemleak-test.c is just a kmemleak test module, which also can not be used
as a built-in kernel module. Thus, i think it may should not be in mm
dir, and move the kmemleak-test.c to samples/kmemleak/kmemleak-test.c.
Fix the spelling of built-in by the way.

Signed-off-by: Hui Su
Signed-off-by: Andrew Morton
Cc: Catalin Marinas
Cc: Jonathan Corbet
Cc: Mauro Carvalho Chehab
Cc: David S. Miller
Cc: Rob Herring
Cc: Masahiro Yamada
Cc: Sam Ravnborg
Cc: Josh Poimboeuf
Cc: Steven Rostedt (VMware)
Cc: Miguel Ojeda
Cc: Divya Indi
Cc: Tomas Winkler
Cc: David Howells
Link: https://lkml.kernel.org/r/20200925183729.GA172837@rlk
Signed-off-by: Linus Torvalds