We just replaced SmallSet<T *, N> with SmallPtrSet<T *, N>, bypassing
the redirection found in SmallSet.h.  With that, we no longer need to
include SmallSet.h in many files.

This patch replaces SmallSet<T *, N> with SmallPtrSet<T *, N>.  Note
that SmallSet.h "redirects" SmallSet to SmallPtrSet for pointer
element types:

  template <typename PointeeType, unsigned N>
class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N>
{};

We only have 140 instances that rely on this "redirection", with the
vast majority of them under llvm/. Since relying on the redirection
doesn't improve readability, this patch replaces SmallSet with
SmallPtrSet for pointer element types.

This is another prune of dead code -- we never generate debug intrinsics
nowadays, therefore there's no need for these codepaths to run.

---------

Co-authored-by: Nikita Popov <github@npopov.com>

This patch changes debugify to support debug variable records, and
subsequently to no longer convert modules automatically to intrinsics
when entering debugify.

Differential Revision: https://reviews.llvm.org/D151424

When a module contains more than one function, we should update debugify metadata
by increasing the number of variables in the function rather than overwritting it.

Previous revert issue is fixed: I forgot to strip all x86-related info from the
test.

Differential Revision: https://reviews.llvm.org/D136949

This brokes some builds
This reverts commit a1bbe8a4e2e50e7100dc17d9ddd1bfc3bfe44977.

When a module contains more than one function, we should update debugify metadata
by increasing the number of variables in the function rather than overwritting it.

Differential Revision: https://reviews.llvm.org/D136949

This is a (fixed) recommit of https://reviews.llvm.org/D121169

after:  1061034926
before: 1063332844

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D121681