When attempting to build Python without dynamic loading (HAVE_DYNAMIC_LOADING is not defined), the module "_imp" will not have the function "exec_dynamic."  However, Lib/bootstrap.py seems to assume that "_imp.exec_dynamic" exists, causing the error:

----
./python -E -S -m sysconfig --generate-posix-vars ;\
if test $? -ne 0 ; then \
	echo "generate-posix-vars failed" ; \
	rm -f ./pybuilddir.txt ; \
	exit 1 ; \
fi
Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1134, in _install
  File "<frozen importlib._bootstrap>", line 1114, in _setup
  File "<frozen importlib._bootstrap>", line 1082, in _builtin_from_name
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 748, in exec_module
AttributeError: module '_imp' has no attribute 'exec_dynamic'
Fatal Python error: Py_Initialize: importlib install failed

Current thread 0x00000000 (most recent call first):
ABNORMAL TERMINATION
generate-posix-vars failed
----

when trying to build.  This error means that Python 3.5 will not be able to build in a purely static (no dynamic loading whatsoever) form.

This error was encountered in Python 3.5b4.