UAPI: strip the _UAPI prefix from header guards during header installation

Strip the _UAPI prefix from header guards during header installation so
that any userspace dependencies aren't affected.  glibc, for example,
checks for linux/types.h, linux/kernel.h, linux/compiler.h and
linux/list.h by their guards - though the last two aren't actually
exported.

  libtool: compile:  gcc -std=gnu99 -DHAVE_CONFIG_H -I. -Wall -Werror -Wformat -Wformat-security -D_FORTIFY_SOURCE=2 -fno-delete-null-pointer-checks -fstack-protector -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i686 -mtune=atom -fasynchronous-unwind-tables -c child.c  -fPIC -DPIC -o .libs/child.o
  In file included from cli.c:20:0:
  common.h:152:8: error: redefinition of 'struct sysinfo'
  In file included from /usr/include/linux/kernel.h:4:0,
  		 from /usr/include/linux/sysctl.h:25,
  		 from /usr/include/sys/sysctl.h:43,
  		 from common.h:50,
  		 from cli.c:20:
  /usr/include/linux/sysinfo.h:7:8: note: originally defined here

Reported-by: Tomasz Torcz <tomek@pipebreaker.pl>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>