DenseSet, SmallPtrSet, SmallSet, SetVector, and StringSet recently
gained C++23-style insert_range.  This patch replaces:

  Dest.insert(Src.begin(), Src.end());

with:

  Dest.insert_range(Src);

This patch does not touch custom begin like succ_begin for now.

Add `Intrinsic::getDeclarationIfExists` to lookup an existing
declaration of an intrinsic in a `Module`.

This adds a type_checked_load_relative intrinsic whose semantics it is to
load a relative function pointer.

A relative function pointer is a pointer to a 32bit value that when
added to its address yields the address of the function.

Differential Revision: https://reviews.llvm.org/D143204

D63932 added a module flag to indicate that we are executing the regular
LTO post merge pipeline, so that GlobalDCE could perform more aggressive
optimization for Dead Virtual Function Elimination. This caused issues
trying to reuse bitcode that had already been through the LTO pipeline
(see context in D139816).

Instead support this by passing down a parameter flag to the
GlobalDCEPass constructor, which is the more usual way for indicating
this information.

Most test changes are to remove incidental uses of this flag. Of the 2
real uses, llvm/test/LTO/ARM/lto-linking-metadata.ll is now obsolete and
removed in this patch, and the virtual-functions-visibility-post-lto.ll
test is updated to use the regular LTO default pipeline where this
parameter is set to true.

Differential Revision: https://reviews.llvm.org/D153655

Mostly removing includes of InitializePasses.h and Pass.h in
passes that no longer has support for the legacy PM.

These are part of the optimization pipeline, of which the legacy pass manager version is deprecated and being removed.

Identified with readability-qualified-auto.

Identified with readability-qualified-auto.