In this PR I'm changing the way we provide the missing functions like
strnlen() on z/OS from the separate header file to a wrapper around the
system headers that declare these functions. This will be less
intrusive.

---------

Co-authored-by: Zibi Sarbinowski <zibi@ca.ibm.com>

This patch removes the C++
disablezOSAutoConversion,enablezOSAutoConversion declarations and also
updates Path.inc to use the common function.

Let the actual syscall error if the file doesn't exist. This produces
a more standard "no such file or directory" phrasing of the error
message,
and avoids an extra step.

The same antipattern appears in the windows code, we should probably
fix that one too.

Only used by Unix/Program.inc and seem always available.

Pull Request: https://github.com/llvm/llvm-project/pull/123288

Pull Request: https://github.com/llvm/llvm-project/pull/123282

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

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

Relands #81708, which was reverted by
f410f74cd5b26319b5796e0404c6a0f3b5cc00a5, now with a corrected unit
test. Origionally the test failed on Windows when run with lit as
`GetConsoleWindow` could not retrieve a window handle regardless of
whether `DetachProcess` was `true` or `false`. The test now uses
`GetStdHandle(STD_OUTPUT_HANDLE)` which does not rely on a console
window existing. Original commit message below.

Adds a new parameter, `bool DetachProcess` with a default option of
`false`, to `llvm::sys::ExecuteNoWait`, which, when set to `true`,
executes the specified program without a controlling terminal.

Functionality added so that the module build daemon can be run without a
controlling terminal.

This reverts commit 86f6caa562255f81b93e72a501a926b17f5ad244. Unit test
was failing on a few windows build bots

Adds a new parameter, `bool DetachProcess` with a default option of
`false`, to `llvm::sys::ExecuteNoWait`, which, when set to `true`,
executes the specified program without a controlling terminal.

Functionality added so that the module build daemon can be run without a
controlling terminal.