Use libraries from local-rust-root directory in configure when using --enable-local-rebuild

When using --enable-local-rebuild configure options, the configure
script will test rustc version. But when running it, it will not use the
libraries in the local-rust-root directory.

So use `LD_LIBRARY_PATH` environment variable to correct it.

Author: semarie

configure

@@ -901,7 +901,7 @@ then
     fi
 
     CMD="${CFG_LOCAL_RUST_ROOT}/bin/rustc${BIN_SUF}"
-    LRV=`$CMD --version`
+    LRV=`LD_LIBRARY_PATH=${CFG_LOCAL_RUST_ROOT}/lib $CMD --version`
     if [ $? -ne 0 ]
     then
         step_msg "failure while running $CMD --version"