I am back at this: (note: short answer to msg277745 - No. does not work for me)

As ... expressed before, this needs to work in three contexts:

2) In-tree testing of build module feature (test_distutils).

Below are results of 'in tree' and 'out of tree' testing. in/out seems to have no (more) impact.
++++
msg219888 also has a patch - that moves the code back to where it originally was: _init_posix

But - same issue - ld_so_aix is not found. (notice the "src" in string of 'threading.py')
[112/401/2] test_distutils
xlc_r: 1501-218 (S) file _configtest.i contains an incorrect file suffix
unable to execute '/opt/lib/python2.7/config/ld_so_aix': No such file or directory
Warning -- os.environ was modified by test_distutils
test test_distutils failed -- multiple errors occurred; run in verbose mode for details
[113/401/3] test_dl
test_dl skipped -- No module named dl
[114/401/3] test_docxmlrpc
/data/prj/python/src/Python-2.7.13/Lib/threading.py:846: DeprecationWarning: sys.exc_clear() not supported in 3.x; use except clauses
  self.__exc_clear()
[115/401/3] test_dumbdbm
root@x064:[/data/prj/python/Python-2.7.13]


Now, back to 'in tree' with patch from msg219888 (no "src" in path)

root@x064:[/data/prj/python/Python-2.7.13]find . -name _sysconfigdata\*.py -ls -exec grep LDSHARED {} \;
48056876   16 -rw-r-----  1 root      1000        15362 Jan 24 15:07 ./build/lib.aix-5.3-2.7/_sysconfigdata.py
 'BLDSHARED': 'Modules/ld_so_aix xlc_r -bI:Modules/python.exp',
 'LDSHARED': '/opt/lib/python2.7/config/ld_so_aix xlc_r -bI:/opt/lib/python2.7/config/python.exp',
[112/401/2] test_distutils
xlc_r: 1501-218 (S) file _configtest.i contains an incorrect file suffix
unable to execute '/opt/lib/python2.7/config/ld_so_aix': No such file or directory
Warning -- os.environ was modified by test_distutils
test test_distutils failed -- multiple errors occurred; run in verbose mode for details
[113/401/3] test_dl
test_dl skipped -- No module named dl
[114/401/3] test_docxmlrpc
/data/prj/python/Python-2.7.13/Lib/threading.py:846: DeprecationWarning: sys.exc_clear() not supported in 3.x; use except clauses
  self.__exc_clear()

Conclusion:
** As the code is - that is removed means the environment variable in sysconfigdata.py is correct,
   I would suggest the patch is to remove the 6 lines there.
   Further, the addition of the code below (per msg219888) has no effect, including it is not needed.

The .dist file is from the source tarball from last december for 2.7.13

michael@x071:[/data/prj/python/src]diff -u  Python-2.7.13/Lib/sysconfig.py.dist>
--- Python-2.7.13/Lib/sysconfig.py.dist 2016-12-17 20:05:06 +0000
+++ Python-2.7.13/Lib/sysconfig.py      2017-01-24 14:56:20 +0000
@@ -307,12 +307,6 @@
             msg = msg + " (%s)" % e.strerror
         raise IOError(msg)

-    # On AIX, there are wrong paths to the linker scripts in the Makefile
-    # -- these paths are relative to the Python source, but when installed
-    # the scripts are in another directory.
-    if _PYTHON_BUILD:
-        vars['LDSHARED'] = vars['BLDSHARED']
-
     # There's a chicken-and-egg situation on OS X with regards to the
     # _sysconfigdata module after the changes introduced by #15298:
     # get_config_vars() is called by get_platform() as part of the
@@ -355,6 +349,11 @@
     # _sysconfigdata is generated at build time, see _generate_posix_vars()
     from _sysconfigdata import build_time_vars
     vars.update(build_time_vars)
+    # On AIX, there are wrong paths to the linker scripts in the Makefile
+    # -- these paths are relative to the Python source, but when installed
+    # the scripts are in another directory.
+    if _PYTHON_BUILD:
+        vars['LDSHARED'] = vars['BLDSHARED']

 def _init_non_posix(vars):
     """Initialize the module as appropriate for NT"""