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>

 # Configuration file for sstrip tool facility

 if OBSOLETE && ! BACKEND && ARCH_BINFMT_ELF

 comment "sstrip"

 config SSTRIP

     bool

     prompt "sstrip (OBSOLETE)"

     help

       The sstrip utility, to maximise the striping of ELF binaries

       (executables and libraries).

       Buildroot version, forked off the original from ELFkickers.

       This one is somewhat maintained by the buildroot guys.

       Supports big-endian systems.

       NOTE! Please read.

         sstrip is now deprecated in crosstool-NG, as it has a few

         shortcomings. For example: it breaks for PPC targets, it

         does not build on non-ELF hosts (eg. mingw32, MacOS-X...).

 endif