Tidy up trap-handling code.

lib/runtime/src/lib.rs

@@ -42,6 +42,8 @@ extern crate cast;
 extern crate failure;
 #[macro_use]
 extern crate failure_derive;
+#[cfg(target_os = "windows")]
+extern crate winapi;
 
 mod export;
 mod imports;

lib/runtime/src/mmap.rs

@@ -130,7 +130,7 @@ impl Drop for Mmap {
         if !self.ptr.is_null() {
             use winapi::um::memoryapi::VirtualFree;
             use winapi::um::winnt::MEM_RELEASE;
-            let r = unsafe { VirtualFree(self.ptr, self.len, MEM_RELEASE) };
+            let r = unsafe { VirtualFree(self.ptr as *mut libc::c_void, self.len, MEM_RELEASE) };
             assert_eq!(r, 0);
         }
     }