Use colon instead of as to cast

README.md

@@ -21,3 +21,25 @@ and a possbility to compile Elna programs for different platforms.
 
 Flex and bison grammar specifications, `lexer.ll` and `parser.yy`, can be found
 in the `boot/` directory.
+
+## Build
+
+The frontend requires GCC 14.2.0 (not tested with other versions).
+
+Download the GCC source. Copy the contents of this repository into `gcc/elna`
+inside GCC. Finally build GCC enabling the frontend with
+`--enable-languages=c,c++,elna`. After the installation the compiler can be
+invoked with `$prefix/bin/gelna`.
+
+There is also a `Rakefile` that downloads, builds and installs GCC into the
+`./build/` subdirectory. The `Rakefile` assumes that ruby and rake, as well as
+all GCC dependencies are already available in the system. It works under Linux
+and Mac OS. In the latter case GCC is patched with the patches used by Homebrew
+(official GCC doesn't support Apple silicon targets). Invoke with
+
+```sh
+rake boot
+```
+
+See `rake -T` for more tasks. The GCC source is under `build/tools`. The
+installation path is `build/host/install`.