Add assertions enabled build of DXC trunk to Compiler Explorer

[llvm-beanz]

During triage it is super helpful to be able to know if input that causes a crash also hits asserts. For this purpose it would be extremely useful to have an asserts-enabled build of DXC on Compiler Explorer. There is an asserts-enabled build of Clang trunk on CE, so this has existing analog.

### Tasks
- [ ] Add DXC asserts enabled build to the build-dxc script (https://github.com/compiler-explorer/misc-builder)
- [ ] Add DXC asserts enabled build to hlsl build configurations (https://github.com/compiler-explorer/infra)
- [ ] Add DXC asserts enabled build to CE (https://github.com/compiler-explorer/compiler-explorer)

[devshgraphicsprogramming]

Would be useful because I've recently pulled the latest master and suddenly this shader produces runtime access violation reading address 0x0000000000000008 but only with a debug build of DXC

https://godbolt.org/z/cPcP17Yze

[devshgraphicsprogramming]

I have my Godbolt own instance and I have a 8 hourly Debug build of DXC

Here's an example of very badly mismatched SPIR-V

(sorry short links don't work yet)

How do I make the asserts print a stack or something instead of just?

Internal compiler error: LLVM Assert
Compiler returned: 3758096385