Actually, I had already done that:

diff --git a/Lib/_aix_support.py b/Lib/_aix_support.py
index 2c5cd3297d..c7f4491633 100644
--- a/Lib/_aix_support.py
+++ b/Lib/_aix_support.py
@@ -12,7 +12,8 @@ try:
     _tmp_bd = get_config_var("AIX_BUILDDATE")
     _bgt = get_config_var("BUILD_GNU_TYPE")
 except ImportError:  # pragma: no cover
-    _have_subprocess = False
+    import _bootsubprocess as subprocess
+    _have_subprocess = True
     _tmp_bd = None
     _bgt = "powerpc-ibm-aix6.1.7.0"

And after that test, I tried with no calls to _aix_support.py

diff --git a/Lib/distutils/util.py b/Lib/distutils/util.py
index 4b002ecef1..513af52ecd 100644
--- a/Lib/distutils/util.py
+++ b/Lib/distutils/util.py
@@ -79,8 +79,9 @@ def get_host_platform():
             machine += ".%s" % bitness[sys.maxsize]
         # fall through to standard osname-release-machine representation
     elif osname[:3] == "aix":
-        from _aix_support import aix_platform
-        return aix_platform()
+        return "%s-%s.%s" % (osname, version, release)
+        # from _aix_support import aix_platform
+        # return aix_platform()
     elif osname[:6] == "cygwin":
         osname = "cygwin"
         rel_re = re.compile (r'[\d.]+', re.ASCII)
diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index 4003726dc9..b116e96007 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -666,8 +666,9 @@ def get_platform():
             machine += ".%s" % bitness[sys.maxsize]
         # fall through to standard osname-release-machine representation
     elif osname[:3] == "aix":
-        from _aix_support import aix_platform
-        return aix_platform()
+        return "%s-%s.%s" % (osname, version, release)
+        # from _aix_support import aix_platform
+        # return aix_platform()
     elif osname[:6] == "cygwin":
         osname = "cygwin"
         import re

±±±±±±±±

So, even when _aix_support.py is not involved at all, _socket.so is being ignored - even though it was built.