These are unneeded even on AIX, PURE_WINDOWS, and ZOS (per #104706)

* HAVE_ERRNO_H: introduced by 1a93330ffa2ae2aa0b49461f05e6f0d51e8443f8 (2009) but unneeded.
  The guarded ABI is unconditionally used by lldb.
* HAVE_FCNTL_H
* HAVE_FENV_H
* HAVE_SYS_STAT_H

Pull Request: https://github.com/llvm/llvm-project/pull/123087

Most systems support strerror_r. For the remaining systems (e.g. MSVC) strerror_s and
strerror can be used as fallbacks. We don't have a supported operating
system/compiler that doesn't provide `strerror`.

Close https://github.com/llvm/llvm-project/issues/62804

https://github.com/flang-compiler/f18/pull/1068 added a fallback
when strerror is unavailable, but I think the code path is dead.

Reviewed By: serge-sans-paille, vzakhari

Differential Revision: https://reviews.llvm.org/D151718

This also includes a few cleanup from Support.

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D121331

The autoconf build system support has been removed a while ago, remove
some outdated references.

Differential Revision: https://reviews.llvm.org/D63608

llvm-svn: 365013

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636

sed -Ei 's/[[:space:]]+$//' include/**/*.{def,h,td} lib/**/*.{cpp,h}

llvm-svn: 338293

I did this a long time ago with a janky python script, but now
clang-format has built-in support for this. I fed clang-format every
line with a #include and let it re-sort things according to the precise
LLVM rules for include ordering baked into clang-format these days.

I've reverted a number of files where the results of sorting includes
isn't healthy. Either places where we have legacy code relying on
particular include ordering (where possible, I'll fix these separately)
or where we have particular formatting around #include lines that
I didn't want to disturb in this patch.

This patch is *entirely* mechanical. If you get merge conflicts or
anything, just ignore the changes in this patch and run clang-format
over your #include lines in the files.

Sorry for any noise here, but it is important to keep these things
stable. I was seeing an increasing number of patches with irrelevant
re-ordering of #include lines because clang-format was used. This patch
at least isolates that churn, makes it easy to skip when resolving
conflicts, and gets us to a clean baseline (again).

llvm-svn: 304787

This reverts commit r265454 since it broke the build.  E.g.:

  http://lab.llvm.org:8080/green/job/clang-stage1-cmake-RA-incremental_build/22413/

llvm-svn: 265459

Some Include What You Use suggestions were used too.

Use anonymous namespaces in source files.

Differential revision: http://reviews.llvm.org/D18778

llvm-svn: 265454

llvm-svn: 223389