[llvm] [llvm] Remove unused includes (NFC) (PR #142733)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

Hi @kazutakahirata 

I think we need to add some includes in Z3Solver.cpp. I get the following when I compile this patch:
```
../lib/Support/Z3Solver.cpp:942:40: error: use of undeclared identifier 'FloatStyle'
  942 |       write_double(OS << K << ": ", V, FloatStyle::Fixed);
      |                                        ^
../lib/Support/Z3Solver.cpp:957:27: error: no member named 'make_scope_exit' in namespace 'llvm'
  957 |   auto StatsGuard = llvm::make_scope_exit([&C, &S] { Z3_stats_dec_ref(C, S); });
      |                     ~~~~~~^
2 errors generated.
```

https://github.com/llvm/llvm-project/pull/142733