config: add an option not to remove the destination directory

In certain circumstances, removing the destination/installation directory
is a bad idea. For example, when the build environment is already taking
care of sanitising the build tree, and pre-installs stuff in there, it is
a very bad idea to remove the destination directory.

This happens now in buildroot, as the crostool-NG backend now installs the
toolchain in the common host-tools directory, and pre-install there a few
host-utilities (eg. host-automake and host-gawk).

Provide a config knob to turn on/off the removal of the destination
directory, defaulting to 'y' (previous behavior), and forced to 'n' when
used as a backend.

Reported-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# This file declares functions to install the kernel headers for mingw

# Copyright 2009 Bart vdr. Meulen

# Licensed under the GPL v2. See COPYING in the root of this package

CT_DoKernelTupleValues() {

    CT_TARGET_KERNEL="mingw32"

    CT_TARGET_SYS=

}

do_kernel_get() {

    CT_GetFile "w32api-${CT_W32API_VERSION}-mingw32-src" \

        http://downloads.sourceforge.net/sourceforge/mingw

}

do_kernel_extract() {

    CT_Extract "w32api-${CT_W32API_VERSION}-mingw32-src"

}

do_kernel_headers() {

    CT_DoStep INFO "Installing kernel headers"

    mkdir -p "${CT_HEADERS_DIR}"

    cp -r ${CT_SRC_DIR}/w32api-${CT_W32API_VERSION}-mingw32/include/* \

          ${CT_HEADERS_DIR}

    CT_EndStep

}