Refine comment in build-toolchain.sh

Author: MaxDesiatov

utils/webassembly/build-toolchain.sh

@@ -72,8 +72,8 @@ sed -i -e "s@\".*/include@\"../../../../share/wasi-sysroot/include@g" $TMP_DIR/$
 
 # Copy nightly-toolchain's host environment stdlib into toolchain
 
-# Avoid to copy usr/lib/swift/clang because our toolchain's one is a directory
-# but nightly's one is symbolic link, so fail to merge them.
+# Avoid copying usr/lib/swift/clang because our toolchain's one is a directory
+# but nightly's one is symbolic link, simple copy fails to merge them.
 rsync -a $NIGHTLY_TOOLCHAIN/usr/lib/ $TMP_DIR/$TOOLCHAIN_NAME/usr/lib/ --exclude 'swift/clang'
 
 $UTILS_PATH/build-foundation.sh $TMP_DIR/$TOOLCHAIN_NAME