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>

# Menu for the cross GDB

config STATIC_TOOLCHAIN

    select GDB_CROSS_STATIC if GDB_CROSS

config GDB_CROSS

    bool

    prompt "Cross-gdb"

    default y

    select GDB_GDBSERVER if ! BARE_METAL

    help

      Build and install a cross-gdb for the target, to run on host.

if GDB_CROSS

config GDB_CROSS_STATIC

    bool

    prompt "Build a static cross gdb"

    default n

    help

      A static cross gdb can be usefull if you debug on a machine that is

      not the one that is used to compile the toolchain.

      That way, you can share the cross-gdb without installing a toolchain

      on every machine that will be used to debug target programs.

endif # GDB_CROSS