gcc4: disable __compiletime_object_size for GCC 4.6+

gcc4: disable __compiletime_object_size for GCC 4.6+

__builtin_object_size is known to be broken on gcc 4.6+.
See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48880 for details.

This causes unnecssary build warnings and errors such as

  In function 'copy_from_user', inlined from 'sb16_copy_from_user'
	at sound/oss/sb_audio.c:878:22:
  arch/x86/include/asm/uaccess_32.h:211:26: error: call to 'copy_from_user_overflow'
	declared with attribute error: copy_from_user() buffer size is not provably correct
  make[3]: [sound/oss/sb_audio.o] Error 1 (ignored)

Disable it where broken.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>