[IRSim][IROutliner] Limit to extracting regions that only require

inputs.

Extracted regions can have both inputs and outputs.  In addition, the
CodeExtractor removes inputs that are only used in llvm.assumes, and
sunken allocas (values are used entirely in the extracted region as
denoted by lifetime intrinsics).  We also cannot combine sections that
have different constants in the same structural location, and these
constants will have to elevated to argument. This patch limits the
extracted regions to those that only require inputs, and do not have any
 other special cases.

We test that we do not outline the wrong constants in:
test/Transforms/IROutliner/outliner-different-constants.ll
test/Transforms/IROutliner/outliner-different-globals.ll
test/Transforms/IROutliner/outliner-constant-vs-registers.ll

We test that correctly outline in:
test/Transforms/IROutliner/outlining-same-globals.ll
test/Transforms/IROutliner/outlining-same-constants.ll
test/Transforms/IROutliner/outlining-different-structure.ll

Reviewers: paquette, plofti

Differential Revision: https://reviews.llvm.org/D86977