On Unix, C extensions are no longer linked to libpython.

It is now possible to load a C extension built using a shared library
Python with a statically linked Python.

When Python is embedded, libpython must not be loaded with
RTLD_LOCAL, but RTLD_GLOBAL instead. Previously, using RTLD_LOCAL, it
was already not possible to load C extensions which were not linked
to libpython, like C extensions of the standard library built by the
"*shared*" section of Modules/Setup.

distutils, python-config and python-config.py have been modified.

bpo-28552, bpo-7774: Fix distutils.sysconfig if sys.executable is
None or an empty string: use os.getcwd() to initialize project_base.

Fix also the distutils build command: don't use sys.executable if
it's evaluated as false (None or empty string).

shutil.which() and distutils.spawn.find_executable() now use
os.confstr("CS_PATH") if available instead of os.defpath, if the PATH
environment variable is not set.

Don't use os.confstr("CS_PATH") nor os.defpath if the PATH
environment variable is set to an empty string to mimick Unix 'which'
command behavior.

Changes:

* find_executable() now starts by checking for the executable in the
  current working directly case. Add an explicit
  "if not path: return None".
* Add tests for PATH='' (empty string), PATH=':' and for PATHEXT.

Set CUSTOMIZED_OSX_COMPILER to True to disable
_osx_support.customize_compiler().

The test test_customize_compiler() now mocks all sysconfig variables
and all environment variables used by customize_compiler().

Fix CFLAGS in customize_compiler() of distutils.sysconfig: when the
CFLAGS environment variable is defined, don't override CFLAGS variable with
the OPT variable anymore.

Initial patch written by David Malcolm.
Co-Authored-By: David Malcolm <dmalcolm@redhat.com>

For C++ extensions, distutils tries to replace the C compiler with the
C++ compiler, but it assumes that C compiler is the first element after
any environment variables set. On AIX, linking goes through ld_so_aix,
so it is the first element and the compiler is the next element. Thus
the replacement is faulty:

ld_so_aix gcc ... -> g++ gcc ...

Also, it assumed that self.compiler_cxx had only 1 element or that
there were the same number of elements as the linker has and in the
same order. This might not be the case, so instead concatenate
everything together.

Command line options for the xlc compiler behave differently from gcc and clang,
so skip this test case for now when xlc is the compiler.

Patch by aixtools (Michael Felt)

check_environ() of distutils.utils now catchs KeyError on calling
pwd.getpwuid(): don't create the HOME environment variable in this
case.

platform.dist() is deprecated and slated for removal in Python 3.8. The
upload command itself should also not be used to upload to PyPI, but
while it continues to exist it should not use deprecated functions.

Two kind of mistakes:

1. Missed space. After concatenating there is no space between words.

2. Missed comma. Causes unintentional concatenating in a list of strings.

Use "backslashreplace" instead of "unicode-escape".  It is not
implementation depended and escapes only non-encodable characters.

Also simplify the code.

In distutils.command.install, replace "pliant children" (previously,
it was "pliant slaves") with "helpers".

<!-- issue-number: [bpo-34605](https://www.bugs.python.org/issue34605) -->
https://bugs.python.org/issue34605
<!-- /issue-number -->

This caused installation errors in some cases on Windows.
Patch by Julien Malard.

* Replace "master process" with "parent process"
* Replace "master option mappings" with "main option mappings"
* Replace "master pattern object" with "main pattern object"
* ssl: replace "master" with "server"
* And some other similar changes

distutils.spawn.find_executable() now falls back on os.defpath if the
PATH environment variable is not set.

bpo-32430: Rename Modules/Setup.dist to Modules/Setup

Remove the necessity to copy the former manually to the latter when updating the local source tree.

Patch by Bo Bayles.

CRT v142 is binary compatible with CRT v140.

* Rather than raise TypeError, warn and call list() on the value.

* Fix tests, revise NEWS and whatsnew text.

* Revise documentation, a string is okay as well.

* Ensure 'requires' and 'obsoletes' are real lists.

* Test that requires and obsoletes are turned to lists.

Revert distutils changes of the commit
696b501cd11dc429a0f661adeb598bfaf89e4112 and remove the realm
variable.