fix fileErrno on node

- adds missing cases and fixes fallback values
- fix sign of getErrno

support/js/support_system.js

@@ -21,5 +21,5 @@ function support_system_unsetEnv(name) {
 }
 
 function support_system_getErrno() {
-  return process.__lasterr===undefined?0:process.__lasterr.errno || 0
+  return process.__lasterr === undefined ? 0 : -process.__lasterr.errno || 0
 }

support/js/support_system_file.js

@@ -1,19 +1,23 @@
 const support_system_file_fs = require('fs')
 const support_system_file_child_process = require('child_process')
 
+// See System/File/Error.idr for return values
 function support_system_file_fileErrno(){
   const n = process.__lasterr===undefined?0:process.__lasterr.errno || 0
   if (process.platform == 'win32') {
-    // TODO: Add the error codes for the other errors
     switch(n) {
+      // these are documented in include/uv/errno.h of libuv
       case -4058: return 2
+      case -4092: return 3
       case -4075: return 4
-      default: return -n
+      default: return -n + 5
     }
   } else {
     switch(n){
+      case -2: return 2
+      case -13: return 3
       case -17: return 4
-      default: return -n
+      default: return -n + 5
     }
   }
 }