In r358396 I merged llvm upstream commit 2e24219d3, which fixed "error:
unsupported relocation on symbol" when assembling arm 'adr' pseudo
instructions. However, the upstream commit did not take big-endian arm
into account.

Applying the same changes to the big-endian handling is straightforward,
thanks to Andrew Turner and Peter Smith for the hint. This will also be
submitted upstream.

MFC after: immediately, since this fix is meant for stable/11