Don't include alignment padding in BBInfo.Size.

Compute alignment padding before and after basic blocks dynamically.

Heed basic block alignment.

This simplifies bookkeeping because we don't have to constantly add and
remove padding from BBInfo.Size.  It also makes it possible to track the
extra known alignment bits we get after a tBR_JTr terminator and when
entering an aligned basic block.

This makes the ARMConstantIslandPass aware of aligned basic blocks.

It is tricky to model block alignment correctly when dealing with inline
assembly and tBR_JTr instructions that have variable size.  If inline
assembly turns out to be smaller than expected, that may cause following
alignment padding to be larger than expected.  This could cause constant
pool entries to move out of range.

To avoid that problem, we use the worst case alignment padding following
inline assembly. This may cause slightly suboptimal constant island
placement in aligned basic blocks following inline assembly.  Normal
functions should be unaffected.

llvm-svn: 146118