NFC: Enable assertions for debug builds

[tex3d]

This change enables assertions for debug builds. LLVM_ENABLE_ASSERTIONS must be enabled explicitly, even for Debug builds, otherwise, it will set NDEBUG, which disables assertions.

[llvm-beanz]

We do default this On for Debug builds: https://github.com/microsoft/DirectXShaderCompiler/blob/main/CMakeLists.txt#L313

Do you know why that isn't working? Seems like we should understand that problem rather than changing the pipelines to work around a potentially bigger issue.

[tex3d]

This change enables assertions for debug builds. LLVM_ENABLE_ASSERTIONS must be enabled explicitly, even for Debug builds, otherwise, it will set NDEBUG, which disables assertions.

Thanks @llvm-beanz - you're right.

I was thinking that the asserts were disabled when I it looked like something should have asserted in the pipeline, and I saw the code in HandleLLVMOptions.cmake, not realizing LLVM_ENABLE_ASSERTIONS was separately set based on debug build type in CMakeLists.txt.