python: export CC + CCSHARED env vars to cross-compile Python C extensions properly

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: do not install pyconfig.h on the target

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: add PYTHON_INC_DIR var to CPPFLAGS

The target's PYTHON_INC_DIR should take precedence over the host's
include dir when cross-compiling.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: add LD and LDSHARED env vars to Build/Compile/PyMod

Tells the host Python to use the target's linker.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: enable shared python lib; make this the norm

This will reduce the bloat when users will want to compile in their
Python C extensions.
There will be a initial bloat (several kb) if just Python
is installed, but that will be compensated when users will add more
C extensions.

During the build we also have to add Python's PKG_BUILD_DIR
so that the shared lib is found when compiling Python's
built-in C extensions.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: add _PYTHON_HOST_PLATFORM env var when cross-compiling C extensions

This mostly helps to avoid confusion when modules are cross-compiled.
Otherwise build folders are named with the host's platform name.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
python: use libncursesw instead of libncurses

Python's build scripts prefer ncursesw, and if it is detected
it will be used.
The problem will occur when linking, since ncursesw libs may not be
installed if not added as deps, but the sources will be compiled
against ncursesw.

Reference from Python's HISTORY file:
  Patch #1428494: Prefer linking against ncursesw over ncurses library.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Merge pull request #445 from commodo/python-update-2

Python update 2