[PATCH build] overriding configure test results

[Ralf Wildenhues]

FYI, syncing the patch below from GCC to src.

The new variables have been documented in gcc/doc/install.texi,
please speak up if you would like documentation in files below
src as well.

Thanks,
Ralf

* Ralf Wildenhues wrote on Sat, Oct 02, 2010 at 11:29:16AM CEST:
> Allow to pass separate configure arguments for build, host and target.
> 
> ChangeLog:
> 2010-10-02  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
> 
> 	PR bootstrap/45326
> 	PR bootstrap/45174
> 	* configure.ac: Honor initial values of $build_configargs,
> 	$host_configargs, $target_configargs.  Mark the precious, so
> 	environment settings get recorded.
> 	* configure: Regenerate.

> diff --git a/configure.ac b/configure.ac
> index 6ef9df6..5f80aa9 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -2969,10 +2969,18 @@ if test "$silent" = yes; then
>  fi
>  baseargs="$baseargs --disable-option-checking"
>  
> +# Record and document user additions to sub configure arguments.
> +AC_ARG_VAR([build_configargs],
> +	   [additional configure arguments for build directories])
> +AC_ARG_VAR([host_configargs],
> +	   [additional configure arguments for host directories])
> +AC_ARG_VAR([target_configargs],
> +	   [additional configure arguments for target directories])
> +
>  # For the build-side libraries, we just need to pretend we're native,
>  # and not use the same cache file.  Multilibs are neither needed nor
>  # desired.
> -build_configargs="--cache-file=../config.cache ${baseargs}"
> +build_configargs="$build_configargs --cache-file=../config.cache ${baseargs}"
>  
>  # For host modules, accept cache file option, or specification as blank.
>  case "${cache_file}" in
> @@ -2986,9 +2994,9 @@ esac
>  
>  # Host dirs don't like to share a cache file either, horribly enough.
>  # This seems to be due to autoconf 2.5x stupidity.
> -host_configargs="--cache-file=./config.cache ${extra_host_args} ${baseargs}"
> +host_configargs="$host_configargs --cache-file=./config.cache ${extra_host_args} ${baseargs}"
>  
> -target_configargs=${baseargs}
> +target_configargs="$target_configargs ${baseargs}"
>  
>  # Passing a --with-cross-host argument lets the target libraries know
>  # whether they are being built with a cross-compiler or being built