Unset some environment variables for example CROSS_COMPILE and ARCH

Tools makefiles recognize these variable and might use them in an undesirable way. For example CROSS_COMPILE has a predence over toolchain we are building and this for example might cause a big endian toolchain to have little endian standard libraries.

Signed-off-by: Anton Kolesov <akolesov@synopsys.com>
Format lines to wrapped at 80 characters

Previous commit had very long lines. This commit wraps them to be no more that 80 characters long.

Signed-off-by: Anton Kolesov <akolesov@synopsys.com>