Move the wasmtime crate directories form lib/* to wasmtime-*.

This follows a similar change to Cranelift made here:

https://github.com/CraneStation/cranelift/pull/660

wasmtime-runtime/build.rs

@@ -0,0 +1,37 @@
+extern crate bindgen;
+extern crate cmake;
+extern crate regex;
+
+use cmake::Config;
+use regex::Regex;
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    let dst = Config::new("signalhandlers").build();
+
+    println!("cargo:rustc-link-search=native={}", dst.display());
+    println!("cargo:rustc-link-lib=static=SignalHandlers");
+
+    let mut bindings_builder = bindgen::Builder::default()
+        .header("signalhandlers/SignalHandlers.hpp")
+        .whitelist_type("TrapContext")
+        .whitelist_type("jmp_buf")
+        .whitelist_function("EnsureEagerSignalHandlers");
+
+    // If we're compiling for Darwin, compile in extra Darwin support routines.
+    if Regex::new(r"-darwin[[:digit:].]*$")
+        .unwrap()
+        .is_match(&env::var("TARGET").unwrap())
+    {
+        bindings_builder = bindings_builder.whitelist_function("EnsureDarwinMachPorts");
+    }
+
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+
+    bindings_builder
+        .generate()
+        .expect("Unable to generate bindings")
+        .write_to_file(out_path.join("signalhandlers.rs"))
+        .expect("Couldn't write bindings!");
+}