[gcc] Remove old "nc" cases from libstdc++'s configure script

These cases are not used, and were apparently added by changing the
generated file rather than editing the source, configure.ac.
Re-running autoconf 2.59 undoes them.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=660

Review URL: http://codereview.chromium.org/3186025
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 454b721..20803a6 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -4989,7 +4989,7 @@
   fi
   ;;
 
-gnu* | nc)
+gnu*)
   lt_cv_deplibs_check_method=pass_all
   ;;
 
@@ -5027,7 +5027,7 @@
   ;;
 
 # This must be Linux ELF.
-linux* | k*bsd*-gnu | kopensolaris*-gnu | nc)
+linux* | k*bsd*-gnu | kopensolaris*-gnu)
   lt_cv_deplibs_check_method=pass_all
   ;;
 
@@ -15124,7 +15124,7 @@
   # Default to "generic".
   if test $enable_clocale_flag = auto; then
     case ${target_os} in
-      linux* | gnu* | kfreebsd*-gnu | knetbsd*-gnu | nc)
+      linux* | gnu* | kfreebsd*-gnu | knetbsd*-gnu)
         enable_clocale_flag=gnu
         ;;
       darwin* | freebsd*)
@@ -15870,7 +15870,7 @@
   # Default to "new".
   if test $enable_libstdcxx_allocator_flag = auto; then
     case ${target_os} in
-      linux* | gnu* | kfreebsd*-gnu | knetbsd*-gnu | nc)
+      linux* | gnu* | kfreebsd*-gnu | knetbsd*-gnu)
         enable_libstdcxx_allocator_flag=new
         ;;
       *)