kbuild: sync misc scripts with Linux 3.18-rc1

This commit imports some updates in misc scripts from Linux 3.18-rc1.

[1] commit cbb4d3e6510b99522719c5ef0 by Horia Geanta
scripts/kernel-doc: handle object-like macros

[2] commit 164f0d2efaaef83 by Michal Marek
kbuild: Fix handling of backslashes in *.cmd files

[3] commit 270a00963cd367214e by Randy Dunlap
scripts/kernel-doc: recognize __meminit

[4] commit a4954fd7724c0f55361eb5 by Masahiro Yamada
  kbuild: remove obj-n and lib-n handling

[5] commit 5b2389b45d1a9c12b9f by Masahiro Yamada
kbuild: simplify build, clean, modbuiltin shorthands

Signed-off-by: Horia Geanta <horia.geanta@freescale.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>