Avoid generating OpPhi on void types, and allow the transformation to
take place on regions that produce pointer and sampled image result
ids if such ids are not used after the region.
Fixes#3787.
Adds a virtual method, GetFreshIds(), to Transformation. Every
transformation uses this to indicate which ids in its protobuf message
are fresh ids. This means that when replaying a sequence of
transformations the replayer can obtain a smallest id that is not in
use by the module already and that will not be used by any
transformation by necessity. Ids greater than or equal to this id
can be used as overflow ids.
Fixes#3851.
Adds a transformation that inserts a conditional statement with a
boolean expression of arbitrary value and duplicates a given
single-entry, single-exit region, so that it is present in each
conditional branch and will be executed regardless of which branch will
be taken.
Fixes#3614.
