windows: fix missing return value warning

Fixes the following warning:

    src\uv-common.c(476): warning C4715:
    'uv__getaddrinfo_translate_error' : not all control paths return
    a value

The function never returns - the final statement is a call to abort() -
but it seems MSVC's program flow analyzer is too weak to figure that
out.

src/uv-common.c

@@ -473,4 +473,5 @@ int uv__getaddrinfo_translate_error(int sys_err) {
   }
   assert(!"unknown EAI_* error code");
   abort();
+  return 0;  /* Pacify compiler. */
 }