python: add patch for distutils to add support for the '_python_sysroot' env var

Patch taken from buildroot:
  http://git.buildroot.net/buildroot/tree/package/python/python-008-distutils-use-python-sysroot.patch

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

lang/python/patches/008-distutils-use-python-sysroot.patch

@@ -0,0 +1,54 @@
+Adjust library/header paths for cross-compilation
+
+When cross-compiling third-party extensions, the get_python_inc() or
+get_python_lib() can be called, to return the path to headers or
+libraries. However, they use the sys.prefix of the host Python, which
+returns incorrect paths when cross-compiling (paths pointing to host
+headers and libraries).
+
+In order to fix this, we introduce the _python_sysroot, _python_prefix
+and _python_exec_prefix variables, that allow to override these
+values, and get correct header/library paths when cross-compiling
+third-party Python modules.
+
+The _python_sysroot variable is also used to prefix the LIBDIR value
+taken from the sysconfigdata module.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+
+Index: b/Lib/distutils/sysconfig.py
+===================================================================
+--- a/Lib/distutils/sysconfig.py
++++ b/Lib/distutils/sysconfig.py
+@@ -19,8 +19,13 @@
+ from distutils.errors import DistutilsPlatformError
+ 
+ # These are needed in a couple of spots, so just compute them once.
+-PREFIX = os.path.normpath(sys.prefix)
+-EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
++if "_python_sysroot" in os.environ:
++    _sysroot=os.environ.get('_python_sysroot')
++    PREFIX = os.path.normpath(_sysroot + os.environ.get('_python_prefix'))
++    EXEC_PREFIX = os.path.normpath(_sysroot + os.environ.get('_python_exec_prefix'))
++else:
++    PREFIX = os.path.normpath(sys.prefix)
++    EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
+ 
+ # Path to the base directory of the project. On Windows the binary may
+ # live in project/PCBuild9.  If we're dealing with an x64 Windows build,
+Index: b/Lib/distutils/command/build_ext.py
+===================================================================
+--- a/Lib/distutils/command/build_ext.py
++++ b/Lib/distutils/command/build_ext.py
+@@ -237,7 +237,10 @@
+         if (sysconfig.get_config_var('Py_ENABLE_SHARED')):
+             if not sysconfig.python_build:
+                 # building third party extensions
+-                self.library_dirs.append(sysconfig.get_config_var('LIBDIR'))
++                libdir = sysconfig.get_config_var('LIBDIR')
++                if "_python_sysroot" in os.environ:
++                    libdir = os.environ.get("_python_sysroot") + libdir
++                self.library_dirs.append(libdir)
+             else:
+                 # building python standard extensions
+                 self.library_dirs.append('.')