[critical] fix Issue 9449 - Static arrays of 128bit types segfault on initializatio...

...n. Incorrect calling of memset128ii

This also exposed a code gen issue with 32 bit OSX SIMD code, also fixed here.

https://issues.dlang.org/show_bug.cgi?id=9449

Requires https://github.com/D-Programming-Language/druntime/pull/901 to be pulled first.