Reapply "[NFC][DebugInfo][DWARF] Create new low-level dwarf library (#…
(#145959)
    
This reapplies cbf781f0bdf2f680abbe784faedeefd6f84c246e, with fixes for
the shared-library build and the unconventional sanitizer-runtime build.

Original Description:

This is the culmination of a series of changes described in [1].
    
Although somewhat large by line count, it is almost entirely mechanical,
creating a new library in DebugInfo/DWARF/LowLevel. This new library has
very minimal dependencies, allowing it to be used from more places than
the normal DebugInfo/DWARF library--in particular from MC.
    
1.
https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665/2

…145081)"

This reverts commit cbf781f0bdf2f680abbe784faedeefd6f84c246e.

Breaks a couple of buildbots.

This is the culmination of a series of changes described in [1].
    
Although somewhat large by line count, it is almost entirely mechanical,
creating a new library in DebugInfo/DWARF/LowLevel. This new library has
very minimal dependencies, allowing it to be used from more places than
the normal DebugInfo/DWARF library--in particular from MC.
    
I am happy to put it in another location, or to structure it differently
if that makes sense. Some have suggested in BinaryFormat, but it is not
a great fit there. But if that makes more sense to the reviewers, I can
do that.
 
Another possibility would be to use pass-through headers to allow
clients who don't care to depend only on DebugInfo/DWARF. This would be
a much less invasive change, and perhaps easier for clients. But also a
system that hides details.

Either way, I'm open.

1.
https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665/2

(Revised version of a previous, unreviewed, PR.)

Move all expression verification into its only client: DWARFVerifier.
Move all printing code (which was a mix of static and member functions)
into a separate class.

This is one in a series of refactoring PRs to separate dwarf
functionality into lower-level pieces usable without object files and
sections at build time. The code is already written this way via various
"if (section == nullptr)" and similar conditionals. So the functionality
itself is needed and exists, but only as a runtime feature. The goal of
these refactors is to remove the build-time dependencies, which will
allow the existing functionality to be used from lower-level parts of
the compiler. Particularly from lib/MC/.... More information at:


https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665

This PR makes verification of .debug_names acceleration table
multithreaded. In local testing it improves verification of clang
.debug_names from four minutes to under a minute.
This PR relies on a current mechanism of extracting DIEs into a vector. 
Future improvements can include creating API to extract one DIE at a
time, or grouping Entires into buckets by CUs and extracting before
parallel step.

Single Thread
4:12.37 real,   246.88 user,    3.54 sys,       0 amem,10232004 mmem
Multi Thread
0:49.40 real,   612.84 user,    515.73 sys,     0 amem, 11226292 mmem

Heterogenous lookups allow us to call find with StringRef, avoiding a
temporary heap allocation of std::string.

To help make better use of dwarfdump verification for identifying and
fixing issues with debug information, the JSON will now emit details
(sub-categories) where relevant. First modification concerns missing
tags as those were recently missing for BOLT debug names.

Test:
test files for JSON output were previously added, so modify here to
expect the new JSON keys. One test has sub-categories and another is
empty.
  ninja check-llvm-tools-llvm-dwarfdump
Also build the tool and run with a local executable to verify.
  ninja llvm-dwarfdump

This reverts commit 13f63010784d8d55620fa7846ac2192f20f95113.
Breaks check-llvm.