compiler/natives/src/reflect: Update mutability of non-exported embedded fields.
compiler/natives/src/reflect: Update mutability of non-exported embedded fields.

Update for upstream changes.

Related to https://github.com/golang/go/commit/6471ace2ea449ea9b7e5b77b9e59c97eafa6392f.
Related to https://github.com/golang/go/commit/d349fa25dfe2a86c01620f8b049c5e78e46759f3.

Fixes:

	=== RUN   TestCallPanic
	--- FAIL: TestCallPanic (0.01s)

	/Users/Dmitri/Dropbox/Work/2013/GoLand/src/github.com/gopherjs/gopherjs/
	test.043844921:1412
	          throw new Error(msg);
	                ^
	Error: did not panic

gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs