hugetlb: replace BUG() with BUILD_BUG() for dummy definitions

hugetlb: replace BUG() with BUILD_BUG() for dummy definitions

The file linux/hugetlb.h has many places where dummy symbols were defined
so that the main source code would contain fewer:

    #ifdef CONFIG_HUGETLBFS

or

    #ifdef CONFIG_TRANSPARENT_HUGEPAGE

If there were any misuse of these symbols, the only symptom would be an
OOPS at runtime.  Change the BUG() to BUILD_BUG() to catch any such abuse
at compile time instead.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: David Rientjes <rientjes@google.com>
Cc: DM <dm.n9107@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>