scripts: leave changelog in build dir, copy to install dir

Users tend to look for the build log in the current working directory,
rather than in the toolchain's installation dir. While bundling the build
log in the toolchain installation dir is nice for distribution and review,
it can be easier to have the build log readily available in the working
directory, as it is quicker to get to it.

So, the build log stays in the working directory until the toolchain is
completely and successfully built, and then a (compressed) copy is made.

Reported-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Options specific to crosstool-NG acting as a backend

config IS_A_BACKEND

    string

    option env="CT_IS_A_BACKEND"

config BACKEND

    bool

    default y if IS_A_BACKEND =  "y" || IS_A_BACKEND =  "Y"

    default n if IS_A_BACKEND != "y" && IS_A_BACKEND != "Y"

config BACKEND_ARCH

    string

    option env="CT_BACKEND_ARCH"

config BACKEND_KERNEL

    string

    option env="CT_BACKEND_KERNEL"

config BACKEND_LIBC

    string

    option env="CT_BACKEND_LIBC"