Stack overflow when compiling for cs_6_6

[damyanp]

See internal bug #55479829 for details until we're able to put an IP-free repro case publicly.

We have a shader that compiles successfully with cs_6_5 but hits a stackoverflow when compiled with cs_6_6 or higher.

[damyanp]

@llvm-beanz found this commit that I was able to hackily port to DXC enough to verify that it does fix the issue:

llvm/llvm-project@9d6d24c