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>

 diff -durN glibc-cvs-2.9.orig/misc/syslog.c glibc-cvs-2.9/misc/syslog.c

 --- glibc-cvs-2.9.orig/misc/syslog.c	2009-06-01 10:16:50.000000000 +0200

 +++ glibc-cvs-2.9/misc/syslog.c	2009-06-01 10:17:20.000000000 +0200

 @@ -152,7 +152,7 @@

  #define	INTERNALLOG	LOG_ERR|LOG_CONS|LOG_PERROR|LOG_PID

  	/* Check for invalid bits. */

  	if (pri & ~(LOG_PRIMASK|LOG_FACMASK)) {

 -		syslog(INTERNALLOG,

 +		__syslog(INTERNALLOG,

  		    "syslog: unknown facility/priority: %x", pri);

  		pri &= LOG_PRIMASK|LOG_FACMASK;

  	}