This AutoConvert.h header frequently gets mislabeled as an unused
include because it is guarded by MVS internally and every usage is also
guarded. This refactors the change to remove this guard and instead make
these functions a noop on other non-z/OS platforms.

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.

This implements the result of the discussion at:

https://discourse.llvm.org/t/rfc-report-fatal-error-and-the-default-value-of-gencrashdialog/73587

There are two different use cases for report_fatal_error, so replace it
with two functions reportFatalInternalError() and
reportFatalUsageError(). The former indicates a bug in LLVM and
generates a crash dialog. The latter does not. The names have been
suggested by rnk and people seemed to like them.

This replaces a lot of the usages that passed an explicit value for
GenCrashDiag. I did not bulk replace remaining report_fatal_error usage
-- they probably require case by case review for which function to use.

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

Identified with misc-include-cleaner.

This patch fixes various errors to enable llvm-lit to run on z/OS

This patch renames the functions in AutoConvert.h/cpp to have a less
generic name because they are z/OS specific.

Originally, tie was introduced by D81156 to flush stdout before writing
to stderr. 030897523 reverted this due to race conditions. Nonetheless,
it does cost performance, causing an extra check in the "cold" path,
which is actually the hot path for raw_svector_ostream. Given that this
feature is only used for errs(), move it to raw_fd_ostream so that it no
longer affects performance of other stream classes.