swift234

Stop reordering blocks in SILBuilder::emitBlock.

This change permits SILGen to make smarter decisions about
block placement by keeping related blocks together instead
of always inserting to the end to the function.  The
flipside is that SILGen needs to be somewhat careful to
create blocks in the right order.  Counter-intuitively,
that order is the reverse of the order in which the blocks
should be laid out, since blocks created later will be
inserted before blocks created earlier.  Note, however,
that this produces the right results for recursive
emission.

To that end, adjust a couple of places in SILGen to
create blocks in properly nested order.

All of the block-order differences in the tests seem
to be desirable; several of them even had confused
comments wondering how on earth a block got injected
where it did.

Also, fix the implementation of SILBuilder::moveBlockTo,
and fix a latent bug in epilogue emission where epilogBB
was erased from its parent (deleting it) and then
queried multiple times (!).

Swift SVN r26428