Rename BLD_HOST_PYTHON_DIR to a more generic name

Rename BLD_HOST_PYTHON_DIR to PYTHON_FOR_WINDOWS_DIR in python-config.sh

Change-Id: I72f82f99e5d3b00b2e5d619e855c16f6f2b4af0d
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/753624


Reviewed-by: Vaseeharan Vinayagamoorthy <vaseeharan.vinayagamoorthy@arm.com>
Tested-by: Service account - used by users in DSG GNU team <dgboter@arm.com>
Reviewed-by: Gianluca Busiello <gianluca.busiello@arm.com>