This patch comes from upstream; it will likely no longer be needed whenever
Python 3.4.2 becomes available.

# HG changeset patch
# Parent 7fafbb7e1a8fbcb8875e25d8cd07273069127556
Issue #21166: Prevent possible segfaults and other random failures of
python --generate-posix-vars in pybuilddir.txt build target by ensuring
that pybuilddir.txt is always regenerated when configure is run and
that the newly built skeleton python does not inadvertently import
modules from previously installed instances.

--- Python-3.4.1/Makefile.pre.in	Mon Aug 11 15:01:28 2014 -0500
+++ Python-3.4.1/Makefile.pre.in	Mon Aug 11 18:16:56 2014 -0700
@@ -557,8 +557,18 @@
 # Create build directory and generate the sysconfig build-time data there.
 # pybuilddir.txt contains the name of the build dir and is used for
 # sys.path fixup -- see Modules/getpath.c.
+# Since this step runs before shared modules are built, try to avoid bootstrap
+# problems by creating a dummy pybuildstr.txt just to allow interpreter
+# initialization to succeed.  It will be overwritten by generate-posix-vars
+# or removed in case of failure.
 pybuilddir.txt: $(BUILDPYTHON)
-	$(RUNSHARED) $(PYTHON_FOR_BUILD) -S -m sysconfig --generate-posix-vars
+	@echo "none" > ./pybuilddir.txt
+	$(RUNSHARED) $(PYTHON_FOR_BUILD) -S -m sysconfig --generate-posix-vars ;\
+	if test $$? -ne 0 ; then \
+		echo "generate-posix-vars failed" ; \
+		rm -f ./pybuilddir.txt ; \
+		exit 1 ; \
+	fi
 
 # Build the shared modules
 # Under GNU make, MAKEFLAGS are sorted and normalized; the 's' for
--- Python-3.4.1/configure.ac	Mon Aug 11 15:01:28 2014 -0500
+++ Python-3.4.1/configure.ac	Mon Aug 11 18:16:56 2014 -0700
@@ -53,6 +53,9 @@
 AC_SUBST(build)
 AC_SUBST(host)
 
+# pybuilddir.txt will be created by --generate-posix-vars in the Makefile
+rm -f pybuilddir.txt
+
 if test "$cross_compiling" = yes; then
     AC_MSG_CHECKING([for python interpreter for cross build])
     if test -z "$PYTHON_FOR_BUILD"; then