Revert "Revert "Revert "cpython: fix finding headers when cross-compiling extension modules"""

This still does not function without issues. E.g., bootstrapped-pip fails with Python 3.6 and 3.7
as well as 3.8 on 32-bit.

Because this is a stdenv-rebuild it needs to be tested significantly better

This reverts commit 6100bc29f7.

pkgs/development/interpreters/python/cpython/3.6/fix-finding-headers-when-cross-compiling.patch

@@ -1,54 +0,0 @@
-From 45dfbbb4f5b67ab83e4365564ea569334e979f8e Mon Sep 17 00:00:00 2001
-From: Ben Wolsieffer <benwolsieffer@gmail.com>
-Date: Fri, 25 Sep 2020 16:49:16 -0400
-Subject: [PATCH] Fix finding headers when cross compiling
-
-When cross-compiling third-party extensions, get_python_inc() may be called to
-return the path to Python's headers. However, it uses the sys.prefix or
-sys.exec_prefix of the build Python, which returns incorrect paths when
-cross-compiling (paths pointing to build system headers).
-
-To fix this, we use the INCLUDEPY and CONFINCLUDEPY conf variables, which can
-be configured to point at host Python by setting _PYTHON_SYSCONFIGDATA_NAME.
-The existing behavior is maintained on non-POSIX platforms or if a prefix is
-manually specified.
----
- Lib/distutils/sysconfig.py | 14 ++++++++++----
- 1 file changed, 10 insertions(+), 4 deletions(-)
-
-diff --git a/Lib/distutils/sysconfig.py b/Lib/distutils/sysconfig.py
-index 2bcd1dd288..567375e488 100644
---- a/Lib/distutils/sysconfig.py
-+++ b/Lib/distutils/sysconfig.py
-@@ -84,8 +84,6 @@ def get_python_inc(plat_specific=0, prefix=None):
-     If 'prefix' is supplied, use it instead of sys.base_prefix or
-     sys.base_exec_prefix -- i.e., ignore 'plat_specific'.
-     """
--    if prefix is None:
--        prefix = plat_specific and BASE_EXEC_PREFIX or BASE_PREFIX
-     if os.name == "posix":
-         if python_build:
-             # Assume the executable is in the build directory.  The
-@@ -98,9 +96,17 @@ def get_python_inc(plat_specific=0, prefix=None):
-             else:
-                 incdir = os.path.join(get_config_var('srcdir'), 'Include')
-                 return os.path.normpath(incdir)
--        python_dir = 'python' + get_python_version() + build_flags
--        return os.path.join(prefix, "include", python_dir)
-+        if prefix is None:
-+          if plat_specific:
-+            return get_config_var('CONFINCLUDEPY')
-+          else:
-+            return get_config_var('INCLUDEPY')
-+        else:
-+          python_dir = 'python' + get_python_version() + build_flags
-+          return os.path.join(prefix, "include", python_dir)
-     elif os.name == "nt":
-+        if prefix is None:
-+          prefix = plat_specific and BASE_EXEC_PREFIX or BASE_PREFIX
-         return os.path.join(prefix, "include")
-     else:
-         raise DistutilsPlatformError(
--- 
-2.28.0
-