Fix build

prepare_libcore.sh

@@ -1,11 +1,20 @@
 #!/bin/bash --verbose
 set -e
 
-SRC_DIR="target/libcore"
-rm -rf $SRC_DIR
-mkdir -p $SRC_DIR/src
-cp -r $(dirname $(rustup which rustc))/../lib/rustlib/src/rust/src/libcore $SRC_DIR/src/libcore || (echo "Please install rust-src component"; exit 1)
-cd $SRC_DIR
+SRC_DIR=$(dirname $(rustup which rustc))"/../lib/rustlib/src/rust/"
+DST_DIR="target/libcore"
+
+if [ ! -e $SRC_DIR ]; then
+    echo "Please install rust-src component"
+    exit 1
+fi
+
+rm -rf $DST_DIR
+mkdir -p $DST_DIR/src
+for crate in libcore libstd; do
+    cp -r $SRC_DIR/src/$crate $DST_DIR/src/
+done
+cd $DST_DIR
 git init
 git add .
 git commit -m "Initial commit" -q