Why would I care if it's portable or not? I've never understood the mentality of "but it's not portable". If something isn't not portable, you put #+ and #- on top of it. I'd rather go for "straight-forward and performant" than for some abstract code transformations to make it runnable on platforms that almost nobody uses to the detriment of everyone else.
LLVM is the lowest common denominator. I'm really not fond of lowest common denominators. (Not to mention the fact that it's bloatware in the first place - it's about twice the size of my favourite compiler, and that's before you add the actual language you're trying to compile.)
Because you literally cannot implement it safely or correctly from the C level on Mac OS X, and any other platform with similar thread/stack/thread-state constraints.
Unless that's a platform you think "nobody uses" ...
LLVM is the lowest common denominator. I'm really not fond of lowest common denominators. (Not to mention the fact that it's bloatware in the first place - it's about twice the size of my favourite compiler, and that's before you add the actual language you're trying to compile.)