(Split of off D67120)
SizeOpts/MachineSizeOpts changes for profile guided size optimization.
(A second try after previously committed as r375254 and reverted as r375375.)
The difference from D69070 is that MachineSizeOptsTest.cpp moved to unittests/Target/X86.
Do you need all these? The tests here don't use GlobalISel Core MC SelectionDAG as far as I can tell (?)
Right. Uploaded D69568 to fix.