[clang] [llvm] [WIP][OpenMP] Remove dependency on `libffi` from offloading runtime (PR #91264)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

I'm unsure how to resolve the issue of `CGF.EmitScalarExpr(NumTeams)` not returning the correct value now. For the following code
```c
#include <stdio.h>
#include <stdlib.h>

int main() {
  int Teams = 10;
#pragma omp target teams distribute parallel for num_teams(Teams)
  for (int i = 0; i < 1; ++i)
    ;

  return 0;
}
```
I get this LLVM-IR, which suggests that it's reading beyond the expected `__context` struct.
```llvm
; Function Attrs: convergent noinline norecurse nounwind optnone uwtable
define weak_odr protected void @__omp_offloading_10302_af886a3_main_l9(ptr noalias noundef %dyn_ptr, ptr noalias noundef %__context) #0 {
entry:
  %dyn_ptr.addr = alloca ptr, align 8
  %__context.addr = alloca ptr, align 8
  %.capture_expr. = alloca i32, align 4
  %0 = call i32 @__kmpc_global_thread_num(ptr @3)
  store ptr %dyn_ptr, ptr %dyn_ptr.addr, align 8
  store ptr %__context, ptr %__context.addr, align 8
  %1 = load ptr, ptr %__context.addr, align 8
  %2 = getelementptr inbounds %struct.anon, ptr %1, i32 0, i32 0
  %3 = load i32, ptr %2, align 4
  store i32 %3, ptr %.capture_expr., align 4
  %4 = load i32, ptr %.capture_expr., align 4
  call void @__kmpc_push_num_teams(ptr @3, i32 %0, i32 %4, i32 0)
  call void (ptr, i32, ptr, ...) @__kmpc_fork_teams(ptr @3, i32 0, ptr @__omp_offloading_10302_af886a3_main_l9.omp_outlined)
  ret void
}
```
Any idea how to resolve this? I'm assuming the way we do this now is no longer valid somehow because of the struct indirection.

https://github.com/llvm/llvm-project/pull/91264