fix Issue 10462 - interface thunk doesn't preserve EBX

Fix http://d.puremagic.com/issues/show_bug.cgi?id=10462

and redo fix for http://d.puremagic.com/issues/show_bug.cgi?id=9729
https://github.com/D-Programming-Language/dmd/commit/e3510d1b801808934ba074b357546960b0bc180e#diff-5cfe3fba587a76d12411a17f8cf22a5eR3123