The 'fake use' asm gadget does not always keep variables alive. E.g., in
rdar://57754659, llvm was unable to preserve two local variables despite
the use of these gadgets. These variables were backed by a LoadInst and
an ExtractValueInst respectively. Instead of emitting shadow copies for
just those kinds of instructions, use shadow copies exclusively. This
may cause more variables to appear in the debugger window before they
are initialized, but should result in fewer variables being dropped.
rdar://57754659
