Unwinds Gone Wild

Don't mix VC runtime and libgcc. These are totally different libraries for doing different job.
VC exception handling is totally incompatible with the way, gcc does exception handling, so,
in any way you won't be able to 'mix' different EH styles.

As for license - why don't bother looking by yourself? It's easy:

I don't see any restrictions with using libgcc in gcc-compiled proprietary software unless
you're doing any modification of its code.

What I meant was that all compiling here is done through Visual
Studio; can the GCC runtime be used for the LLVM generated JIT
program, or not?