Remove alignment from deserted constant islands.

ARMConstantIslandPass may sometimes leave empty constant islands behind
(it really shouldn't). Remove the alignment from the empty islands so
the size calculations are still correct.

This should fix the many Thumb1 assembler errors in the nightly test
suite.

The reduced test case for this problem is way too big. That is to be
expected for ARMConstantIslandPass bugs.

<rdar://problem/10534709>

llvm-svn: 145970