bpo-36302: Sort list of sources (pythonGH-12341)

When building packages (e.g. for openSUSE Linux)
(random) filesystem order of input files
influences ordering of functions in the output .so files.
Thus without the patch, builds (in disposable VMs) would usually differ.

Without this patch, all callers have to be patched individually
ofalk/libdnet#42
sass/libsass-python#212
tahoe-lafs/pycryptopp#41
yt-project/yt#2206
pyproj4/pyproj#142
pytries/datrie#49
Roche/pyreadstat#37
but that is an infinite effort.

See https://reproducible-builds.org/ for why this matters.

Lib/distutils/command/build_ext.py

@@ -490,7 +490,8 @@ def build_extension(self, ext):
                   "in 'ext_modules' option (extension '%s'), "
                   "'sources' must be present and must be "
                   "a list of source filenames" % ext.name)
-        sources = list(sources)
+        # sort to make the resulting .so file build reproducible
+        sources = sorted(sources)
 
         ext_path = self.get_ext_fullpath(ext.name)
         depends = sources + ext.depends

Misc/NEWS.d/next/Library/2019-03-21-19-23-46.bpo-36302.Yc591g.rst

@@ -0,0 +1,2 @@
+distutils sorts source file lists so that Extension .so files
+build more reproducibly by default