Use target triple in cache directory hierarchy (#300)

wasmtime-environ/src/cache.rs

@@ -231,7 +231,7 @@ impl ModuleCacheEntry {
             );
             Some(
                 conf::cache_directory()
-                    .join(isa.name())
+                    .join(isa.triple().to_string())
                     .join(compiler_dir)
                     .join(mod_filename),
             )

wasmtime-runtime/src/mmap.rs

@@ -4,6 +4,7 @@
 use core::ptr;
 use core::slice;
 use errno;
+#[cfg(not(target_os = "windows"))]
 use libc;
 use region;
 use std::string::{String, ToString};