cpython: expose gdb libpython.py

used together with cpython's debugging symbols, this allows inspection of
the python stack of cpython programs in gdb. this file is a little
different from the rest of the python output by this package, in that it's
not intended to be run by the current python being built, instead by the
python being used by the gdb in question, which could be very different.
therefore placed in its own, but hopefully logical & predictable location.

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

@@ -279,6 +279,13 @@ in with passthru; stdenv.mkDerivation {
     find $out -name "*.py" | ${pythonForBuildInterpreter} -OO -m compileall -q -f -x "lib2to3" -i -
     '' + optionalString stripBytecode ''
     find $out -type d -name __pycache__ -print0 | xargs -0 -I {} rm -rf "{}"
+    '' + ''
+    # *strip* shebang from libpython gdb script - it should be dual-syntax and
+    # interpretable by whatever python the gdb in question is using, which may
+    # not even match the major version of this python. doing this after the
+    # bytecode compilations for the same reason.
+    mkdir -p $out/share/gdb
+    sed '/^#!/d' Tools/gdb/libpython.py > $out/share/gdb/libpython.py
   '';
 
   preFixup = stdenv.lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''