Specifically this is the assertion in BasicBlock.cpp. Now that we're not
examining or setting that flag consistently (because it'll be deleted in
about an hour) there's no need to keep this assertion.

Original commit title:

[DebugInfo][RemoveDIs] Remove some debug intrinsic-only codepaths (#143451)

This reverts commit c71a2e688828ab3ede4fb54168a674ff68396f61.

/me squints -- this is hitting an assertion I thought had been deleted,
will revert and investigate for a bit.

These are opportunistic deletions as more places that make use of the
IsNewDbgInfoFormat flag are removed. It should (TM)(R) all be dead code
now that `IsNewDbgInfoFormat` should be true everywhere.

FastISel: we don't need to do debug-aware instruction counting any more,
because there are no debug instructions,
Autoupgrade: you can no-longer avoid autoupgrading of intrinsics to
records
DIBuilder: Delete the code for creating debug intrinsics (!)
LoopUtils: No need to handle debug instructions, they don't exist

This is for consistency with #139401.

In [1], Nikita Popov suggested that during lowering 'unreachable' insn
should not generate extra code for naked functions, and this applies to
all architectures. Note that for naked functions, 'unreachable' insn is
necessary in IR since the basic block needs a terminator to end.

This patch checked whether a function is naked function or not. If it is
a naked function, 'unreachable' insn will not generate ISD::TRAP.

  [1] https://github.com/llvm/llvm-project/pull/131731

Co-authored-by: Yonghong Song <yonghong.song@linux.dev>

This focuses on the common interfaces and tablegen. More changes
are needed to individual targets.

Add operators to Register to supporting adding an offset to get
another Register.