We can pass a range to llvm::fill.

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

The documentation for compare_exchange_weak says that it is allowed to
spuriously fail. If compare_exchange_weak is called in a loop, spurious
failures usually are benign - but in these cases, a spurious failure
would give incorrect behaviour.

E.g. in TypePool::getOrCreateTypeEntryBody, we assume that if the
compare_exchange call returned false, we had been preempted by another
thread and that DIE is non-null.

This fixes running the dsymutil tests on Windows on aarch64 (built with
a mingw toolchain with libc++).

Note that PointerUnion::{is,get} have been soft deprecated in
PointerUnion.h:

  // FIXME: Replace the uses of is(), get() and dyn_cast() with
  //        isa<T>, cast<T> and the llvm::dyn_cast<T>

I'm not touching PointerUnion::dyn_cast for now because it's a bit
complicated; we could blindly migrate it to dyn_cast_if_present, but
we should probably use dyn_cast when the operand is known to be
non-null.

The result of the function cannot be correctly interpreted without
knowing the precise form type (a type signature needs to be looked up
very differently from a supplementary debug info reference). The
function sort of worked because the two reference types (unit-relative
and section-relative) that can be handled uniformly are also the most
common types of references, but this setup made it easy to write code
which does not support other kinds of reference (and if one tried to
support them, the result didn't look pretty --
https://github.com/llvm/llvm-project/pull/97423/files#r1676217081).

The split is based on the reference type classification from DWARFv5
(Section 7.5.5 Classes and Forms), and it should enable uniform (if
slightly more verbose) hadling. Note that this only affects users which
want more control of how (or if) the references are resolved. Users
which just want to access the referenced DIE can use the higher level
API (DWARFDie::GetAttributeValueAsReferencedDie) which returns (or will
return after #97423 is merged) the correct die for all reference types
(except for supplementary references, which we don't support right now).

and reject them when copying Swift interface files, since they can live
outside of DEVELOPER_DIR.

The function was meant to find the Developer/ dir, but it found a
Developer directory nested deep inside the top-level Developer dir.

The new implementation rejects everything in Xcode.app/Developer in
broad strokes.

rdar://128571037