[llvm] [SPIR-V] Replace assert with report_fatal (PR #118617)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> I thought this was an analysis/visitor that is intended to visit the blocks in a certain order. It was used to order the blocks, but that had changed.

:+1: That's the case. `sortBlocks` don't use it anymore. The hang was caused by a death test I added which passed a irreducible to the visitor to make sure it asserted. But if asserts are disabled, this test hang.



https://github.com/llvm/llvm-project/pull/118617