bpo-30604: port fix from 3.6 dropping binary compatibility tweaks

* bpo-30183: Fixes HP-UX cc compilation error in pytime.c

HP-UX does not support the CLOCK_MONOTONIC identifier, and will fail to
compile:

    "Python/pytime.c", line 723: error #2020: identifier
    "CLOCK_MONOTONIC" is undefined
          const clockid_t clk_id = CLOCK_MONOTONIC;

Add a new section for __hpux that calls 'gethrtime()' instead of
'clock_gettime()'.

* bpo-30183: Removes unnecessary return

* bpo-30616: Functional API of enum allows to create empty enums.

* Update NEWS

move addition to avoid conflict

New file: Modules/expat/siphash.h.

Comceptually -> Conceptually

Improve the description of the high and low parameters for set_write_buffer_limits.
Also fixed a small grammatical issue.

* Make PyTraceMalloc_Track() and PyTraceMalloc_Untrack() functions
  public (remove the "_" prefix)
* Remove the _PyTraceMalloc_domain_t type: use directly unsigned
  int.
* Document methods

Note: methods are already tested in test_tracemalloc.

They now always return bytes.

Updated the gettext documentation.

splithost() expects an URL starting with "//" not with "http://".

The current regex based splitting produces a wrong result. For example::

  http://abc#@def

Web browsers parse that URL as ``http://abc/#@def``, that is, the host
is ``abc``, the path is ``/``, and the fragment is ``#@def``.

* Fixes build scripts to find msbuild.exe and stop relying on vcvarsall.bat
Also fixes bdist_wininst.vcxproj to use correct version in generated name.

- removes PY_WARN_ON_C_LOCALE build time flag
- locale coercion and compatibility warnings are now always compiled
  in, but are off by default
- adds PYTHONCOERCECLOCALE=warn runtime option to aid in
  debugging potentially locale related compatibility problems

Due to not-yet-resolved test failures on *BSD systems (including
Mac OS X), this also temporarily disables UTF-8 as a locale coercion
target, and skips testing the interpreter's behavior in the POSIX locale.

elem is the result of .lower() 6 lines above the handle_endtag call.
Patch by Motoki Naruse

This reverts commit 258bfc46.

* bpo-30523: Add --list-cases unittest

* Addressed haypo's request

* Addressed haypo's request

This caused a segfault on eval("f'\\\n'") and eval("f'\\\r'") in debug build.

* bpo-30523: regrtest: Add --list-cases option

* bpo-30523: Enhance --list-cases

* Add get_abs_module() function, use it in list_cases()
* list_cases() now logs skipped tests into stderr

* Remove unused doctest

The Windows build now depends on Python 3.6 to fetch externals, but it will be downloaded via NuGet (which is downloaded via PowerShell) if it is not available via `py -3.6`.  This means the only thing that must be installed on a modern Windows box to do a full build of CPython with all extensions is Visual Studio.

Also fixes an outdated note about _lzma in PCbuild/readme.txt

* test dedent with declining indent level
* add textwrap.dedent test cases

In rare circumstances PyImport_Import() could return NULL without raising
an error.

When os.spawnv() fails while handling arguments, free correctly
argvlist: pass lastarg+1 rather than lastarg to free_string_array()
to also free the first item.

In the C locale on Mac OS X, the default filesystem encoding
used for operating system interfaces is UTF-8, but the
default encoding used on the standard streams is still ASCII.

Setting the POSIX locale also behaves differently from setting
other locales on Mac OS X, so skip that in the test suite for now.

* bpo-29591: Upgrade Modules/expat to libexpat 2.2

* bpo-29591: Restore Python changes on expat

* bpo-29591: Remove expat config of unsupported platforms

Remove the configuration (Modules/expat/*config.h) of unsupported
platforms:

* Amiga
* MacOS Classic on PPC32
* Open Watcom

* bpo-29591: Remove useless XML_HAS_SET_HASH_SALT

The XML_HAS_SET_HASH_SALT define of Modules/expat/expat.h became
useless since our local expat copy was upgrade to expat 2.1 (it's now
expat 2.2.0).

Use a build/ directory in the build directory, not in the source
directory, since the source directory may be read-only and must not
be modified.

Fallback on the source directory if the build directory is not
available (missing "abs_builddir" sysconfig variable).

bpo-30436: Raise ModuleNotFoundError for importlib.util.find_spec() when parent isn't a package (GH-1899)

Previously AttributeError was raised, but that's not very reflective of the fact that the requested module can't be found since the specified parent isn't actually a package.