This is an attempt to reland
https://github.com/llvm/llvm-project/pull/159104 with the fix for
https://github.com/llvm/llvm-project/issues/160197.

The original patch had the following problem: when an abstract
subprogram DIE is constructed from within
`DwarfDebug::endFunctionImpl()`,
`DwarfDebug::constructAbstractSubprogramScopeDIE()` acknowledges `unit:`
field of DISubprogram. But an abstract subprogram DIE constructed from
`DwarfDebug::beginModule()` was put in the same compile unit to which
global variable referencing the subprogram belonged, regardless of
subprogram's `unit:`.

This is fixed by adding `DwarfDebug::getOrCreateAbstractSubprogramCU()`
used by both`DwarfDebug:: constructAbstractSubprogramScopeDIE()` and
`DwarfCompileUnit::getOrCreateSubprogramDIE()` when abstract subprogram
is queried during the creation of DIEs for globals in
`DwarfDebug::beginModule()`.

The fix and the already-reviewed code from
https://github.com/llvm/llvm-project/pull/159104 are two separate
commits in this PR.

=====
The original commit message follows:

With this change, construction of abstract subprogram DIEs is split in
two stages/functions: creation of DIE (in
DwarfCompileUnit::getOrCreateAbstractSubprogramDIE) and its population
with children (in
DwarfCompileUnit::constructAbstractSubprogramScopeDIE).

With that, abstract subprograms can be created/referenced from
DwarfDebug::beginModule, which should solve the issue with static local
variables DIE creation of inlined functons with optimized-out
definitions. It fixes https://github.com/llvm/llvm-project/issues/29985.

LexicalScopes class now stores mapping from DISubprograms to their
corresponding llvm::Function's. It is supposed to be built before
processing of each function (so, now LexicalScopes class has a method
for "module initialization" alongside the method for "function
initialization"). It is used by DwarfCompileUnit to determine whether a
DISubprogram needs an abstract DIE before DwarfDebug::beginFunction is
invoked.

DwarfCompileUnit::getOrCreateSubprogramDIE method is added, which can
create an abstract or a concrete DIE for a subprogram. It accepts
llvm::Function* argument to determine whether a concrete DIE must be
created.

This is a temporary fix for
https://github.com/llvm/llvm-project/issues/29985. Ideally, it will be
fixed by moving global variables and types emission to
DwarfDebug::endModule (https://reviews.llvm.org/D144007,
https://reviews.llvm.org/D144005).

Some code proposed by Ellis Hoag <ellis.sparky.hoag@gmail.com> in
https://github.com/llvm/llvm-project/pull/90523 was taken for this
commit.

Reverts llvm/llvm-project#159104 due to the issues reported in
https://github.com/llvm/llvm-project/issues/160197.

With this change, construction of abstract subprogram DIEs is split in
two stages/functions:
creation of DIE (in DwarfCompileUnit::getOrCreateAbstractSubprogramDIE)
and its population with children (in
DwarfCompileUnit::constructAbstractSubprogramScopeDIE).
With that, abstract subprograms can be created/referenced from
DwarfDebug::beginModule, which should solve the issue with static local
variables DIE creation of inlined functons with optimized-out
definitions. It fixes https://github.com/llvm/llvm-project/issues/29985.

LexicalScopes class now stores mapping from DISubprograms to their
corresponding llvm::Function's. It is supposed to be built before
processing of each function (so, now LexicalScopes class has a method
for "module initialization" alongside the method for "function
initialization"). It is used by DwarfCompileUnit to determine whether a
DISubprogram needs an abstract DIE before DwarfDebug::beginFunction is
invoked.

DwarfCompileUnit::getOrCreateSubprogramDIE method is added, which can
create an abstract or a concrete DIE for a subprogram. It accepts
llvm::Function* argument to determine whether a concrete DIE must be
created.

This is a temporary fix for
https://github.com/llvm/llvm-project/issues/29985. Ideally, it will be
fixed by moving global variables and types emission to
DwarfDebug::endModule (https://reviews.llvm.org/D144007,
https://reviews.llvm.org/D144005).

Some code proposed by Ellis Hoag <ellis.sparky.hoag@gmail.com> in
https://github.com/llvm/llvm-project/pull/90523 was taken for this
commit.

TPC is only used to access the option `ShouldEmitDebugEntryValues`.

Many of these are indexing BitVectors or something where we can't
using MCRegister and need the register number.

Identified with misc-include-cleaner.

This patch handles virtual registers in the VarLocBasedImpl of the
LiveDebugVariables pass, allowing it to be used on architectures that
depend on virtual registers in debugging, like NVPTX. It enables the
pass for NVPTX.

These would implicitly cast the register to `unsigned`. Switch most of
them to use printReg will give a more readable output. Change some
others to use Register::id() so we can eventually remove the implicit
cast to `unsigned`.