kbuild: fix "Argument list too long" error for "make headers_check",

I'm trying to install kernel headers to build a cross-toolchain, but got
the following:

make ARCH=arm
INSTALL_HDR_PATH=/work/psl/eldk-builds/arm-2009-04-21/work/var/tmp/crosstool-0.43-3-root/usr/crosstool/gcc-4.2.2-glibc-20070515T2025-eldk/
+arm-linux-gnueabi/arm-linux-gnueabi/
headers_check
...
  CHECK   include/linux/raid (2 files)
  CHECK   include/linux/spi (1 files)
  CHECK   include/linux/sunrpc (1 files)
  CHECK   include/linux/tc_act (6 files)
  CHECK   include/linux/tc_ematch (4 files)
  CHECK   include/linux/usb (8 files)
make[2]: execvp: /bin/sh: Argument list too long
make[2]: ***
[/work/psl/eldk-builds/arm-2009-04-21/work/var/tmp/crosstool-0.43-3-root/usr/crosstool/gcc-4.2.2-glibc-20070515T2025-eldk/arm-linux-gnueab
+i/arm-linux-gnueabi//include/linux/.check]
Error 127
make[1]: *** [linux] Error 2
make: *** [headers_check] Error 2
->

Introduce use of xargs to fix this.

Signed-off-by: Sergei Poselenov <sposelenov@emcraft.com>
Cc: Wolfgang Denk <wd@denx.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>