Add initial support for *-*-nacl target.

configure

 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.60 for llvm 3.0svn.
 #
 # Report bugs to <llvmbugs@cs.uiuc.edu>.
 #
 # Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
 # 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
 # This configure script is free software; the Free Software Foundation
 # gives unlimited permission to copy, distribute and modify it.
@@ skipping 2323 matching lines @@
   *-*-auroraux*)
     llvm_cv_target_os_type="AuroraUX" ;;
   *-*-win32*)
     llvm_cv_target_os_type="Win32" ;;
   *-*-mingw*)
     llvm_cv_target_os_type="MingW" ;;
   *-*-haiku*)
     llvm_cv_target_os_type="Haiku" ;;
   *-*-rtems*)
     llvm_cv_target_os_type="RTEMS" ;;
+  *-*-nacl*)
+    llvm_cv_target_os_type="NativeClient" ;;
   *-unknown-eabi*)
     llvm_cv_target_os_type="Freestanding" ;;
   *)
     llvm_cv_target_os_type="Unknown" ;;
 esac
 fi
 { echo "$as_me:$LINENO: result: $llvm_cv_target_os_type" >&5
 echo "${ECHO_T}$llvm_cv_target_os_type" >&6; }
 
 if test "$llvm_cv_os_type" = "Unknown" ; then
@@ skipping 21887 matching lines @@
            --cache-file=\"\$ac_sub_cache_file\" --srcdir=\"\$ac_srcdir\"" ||
         { { echo "$as_me:$LINENO: error: $ac_sub_configure failed for $ac_dir" >&5
 echo "$as_me: error: $ac_sub_configure failed for $ac_dir" >&2;}
    { (exit 1); exit 1; }; }
     fi
 
     cd "$ac_popdir"
   done
 fi