python2 and python3: build unoptimized bytecode again

In 9d03ff5222 I made the CPython builds
reproducible. This required not generating default unoptimized bytecode.
I was under the impression the optimized bytecode would be used then,
but you need to opt-in on that. Not having the default bytecode resulted
in a significant performance hit. Therefore, bytecode is generated again
in this commit, and thereby the builds are no longer reproducible.

https://bugs.python.org/issue29708
(cherry picked from commit 23e348bfe2b161e761dd37e3be86a807f3cd6f94)

pkgs/development/interpreters/python/cpython/2.7/default.nix

@@ -27,9 +27,9 @@
 , sha256
 , passthruFun
 , static ? false
-, stripBytecode ? reproducibleBuild
+, stripBytecode ? true
 , rebuildBytecode ? true
-, reproducibleBuild ? true
+, reproducibleBuild ? false
 , enableOptimizations ? false
 , pythonAttr ? "python${sourceVersion.major}${sourceVersion.minor}"
 }:
@@ -48,6 +48,8 @@ assert lib.assertMsg (reproducibleBuild -> stripBytecode)
 assert lib.assertMsg (reproducibleBuild -> (!enableOptimizations))
   "Deterministic builds are not achieved when optimizations are enabled.";
 
+assert lib.assertMsg (reproducibleBuild -> (!rebuildBytecode))
+  "Deterministic builds are not achieved when (default unoptimized) bytecode is created.";
 
 with lib;
 
@@ -296,8 +298,10 @@ in with passthru; stdenv.mkDerivation ({
         # First we delete all old bytecode.
         find $out -name "*.pyc" -delete
         '' + optionalString rebuildBytecode ''
-        # Then, we build for the two optimization levels.
-        # We do not build unoptimized bytecode, because its not entirely deterministic yet.
+        # We build 3 levels of optimized bytecode. Note the default level, without optimizations,
+        # is not reproducible yet. https://bugs.python.org/issue29708
+        # Not creating bytecode will result in a large performance loss however, so we do build it.
+        find $out -name "*.py" | ${pythonForBuildInterpreter} -m compileall -q -f -x "lib2to3" -i -
         find $out -name "*.py" | ${pythonForBuildInterpreter} -O  -m compileall -q -f -x "lib2to3" -i -
         find $out -name "*.py" | ${pythonForBuildInterpreter} -OO -m compileall -q -f -x "lib2to3" -i -
       '' + optionalString stdenv.hostPlatform.isCygwin ''