[sledge] Translate `invoke abort` to `abort`

Summary:
Sometimes calls to the `abort` C stdlib function appear as `invoke`
instructions in LLVM. They should be translated to the LLAIR abort
instruction just like the non-raising `call abort` case.

Reviewed By: kren1

Differential Revision: D15706574

fbshipit-source-id: 1509ed0e3

sledge/src/llair/frontend.ml

@@ -1037,6 +1037,8 @@ let xlate_instr :
       | ["__llair_throw"] ->
           let dst = Llair.Jump.mk unwind_dst args in
           emit_term (Llair.Term.goto ~dst ~loc)
+      | ["abort"] ->
+          emit_term ~prefix:[Llair.Inst.abort ~loc] Llair.Term.unreachable
       | ["_Znwm" (* operator new(size_t num) *)]
        |[ "_ZnwmSt11align_val_t"
           (* operator new(unsigned long num, std::align_val_t) *) ]