Fix toplevel 'config.status --recheck' for --enable-lto.

[Ralf Wildenhues <Ralf dot Wildenhues at gmx dot de>]

Currently, when rebuilding the tree after toplevel configure changed,
and lto was enabled, the triggered './config.status --recheck' fails
with:

  checking for the correct version of libelf... yes
  configure: error: 
  The following requested languages could not be built: lto
  Supported languages are: c,c++,fortran,java,lto,objc,obj-c++
  make: *** [config.status] Error 1

which happens because the language loop from the previous configure run
added another 'lto' to the --enable-languages command passed to
configure by config.status (--enable-languages does not allow languages
listed multiple times).  The patch below fixes that.

Tested by running the following sequence of commands
  ../toplevel/configure $args
  ./config.status --recheck
  ./config.status --recheck

with args containing all possible combinations of
  '' | --enable-lto | --disable-lto

with a few combinations of
  --enable-languages=...

and with either a working, or a defunct installation of libelf in place,
and ensuring things work as expected most of the time, except for:
passing

  --enable-languages=...,lto,...

will act as if lto was not passed in this argument (thus only care for
presence of --{en,dis}able-lto).  Thoughts on whether it should do
something different, and if yes, what, or whether install.texi should be
adjusted?  It currently states

  @item --enable-languages=@var{lang1},@var{lang2},@dots{}
  Specify that only a particular subset of compilers and
  their runtime libraries should be built.  For a list of valid values for
  @var{langN} you can issue the following command in the
  @file{gcc} directory of your GCC source tree:@*
  @smallexample
  grep language= */config-lang.in
  @end smallexample
  Currently, you can use any of the following:
  @code{all}, @code{ada}, @code{c}, @code{c++}, @code{fortran}, @code{java},
  @code{objc}, @code{obj-c++}.

Otherwise, OK for trunk (and sync to src)?

Thanks,
Ralf

Fix toplevel 'config.status --recheck' for --enable-lto.

ChangeLog:
2009-10-11  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>

	* configure.ac: Add 'lto' to enable_languages, not
	new_enable_languages, and only if not already present.
	* configure: Regenerate.

diff --git a/configure.ac b/configure.ac
index bc2e593..e11035e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1845,7 +1845,10 @@ if test -d ${srcdir}/gcc; then
   # If LTO is enabled, add the LTO front end.
   extra_host_libiberty_configure_flags=
   if test "$enable_lto" = "yes" ; then
-    new_enable_languages="${new_enable_languages}lto,"
+    case ,${enable_languages}, in
+      *,lto,*) ;;
+      *) enable_languages="${enable_languages},lto" ;;
+    esac
     if test "${ENABLE_GOLD}" = "yes" ; then
       configdirs="$configdirs lto-plugin"
       extra_host_libiberty_configure_flags=--enable-shared