[dunecontrol,bugfix] Make compiler error during multiarch detection non-fatal again.

The compiler might exit with nonzero exit code if given non-existent
options. Therefore we need to use set +e during this to make dunecontrol
to continue running even the options are not supported.

bin/dunecontrol

@@ -233,7 +233,7 @@ extract_multiarch(){
     my_cxx_compiler=`echo $CONFIGURE_FLAGS | $GREP CXX| sed "s/.*CXX=[\"']\?\([$NOBLANK^'^\"]*\)[\"']\?.*/\1/"`
   fi
   if test "x$my_cxx_compiler" == "x"; then
-    set +e
+    set +e #error in the multiarch detection should not be fatal.
     $(which cc &>/dev/null)
     if test $? -eq "0"; then
       my_cxx_compiler=cc
@@ -241,11 +241,11 @@ extract_multiarch(){
       my_cxx_compiler=gcc
     fi
   fi
-  set -e
   multiarch=$($my_cxx_compiler --print-multiarch 2>/dev/null)
   if test $? -gt 0; then
     multiarch=$($my_cxx_compiler -v 2>&1| $GREP target | sed "s/.*target=\([a-z0-9_-]\+\)/\1/")
   fi
+  set -e # set to old value.
   export MULTIARCH_LIBDIR="lib/$multiarch"
 }