Update hello-world host

examples/hello-world/platform/host/README.md

@@ -0,0 +1,18 @@
+# Rebuilding the host from source
+
+Here are the current steps to rebuild this host. 
+
+> This is a C host, which is the simplest to build.
+> For an example of a Rust host, see the quicksort example.
+
+First, `cd` into `host/src/` and rebuild `host.o` like so:
+
+```
+$ clang -c host.c -o host.o
+```
+
+Next, move `host.o` into the appropriate `platform/` subdirectory
+based on your architecture and operating system. For example,
+on macOS, you'd move `host.o` into the `platform/host/x86_64-unknown-darwin10/` directory.
+
+Congratulations! You now have an updated host.

examples/hello-world/platform/host/src/host.rs

@@ -1,23 +0,0 @@
-#![crate_type = "staticlib"]
-
-use std::ffi::CStr;
-use std::os::raw::c_char;
-
-extern "C" {
-    #[link_name = "main_1"]
-    fn str_from_roc() -> *const c_char;
-}
-
-// This magical #[export_name] annotation seems to be the only way to convince
-// LLVM to emit this as the symbol "start" rather than "_start" on macOS.
-// The linker will not recognize "_start" as the program entrypoint.
-//
-// See https://github.com/rust-lang/rust/issues/35052#issuecomment-235420755
-#[export_name = "\x01start"]
-pub extern "C" fn main(_argc: isize, _argv: *const *const u8) -> isize {
-    let c_str = unsafe { CStr::from_ptr(str_from_roc()) };
-
-    println!("Roc says: \"{}\"", c_str.to_str().unwrap());
-
-    0
-}