llgo/ssa: use b.CreateUnreachable to panic

internal/runtime/llgo_autogen.ll

@@ -78,7 +78,7 @@ _llgo_1:                                          ; preds = %_llgo_0
 
 _llgo_2:                                          ; preds = %_llgo_0
   %10 = call %"github.com/goplus/llgo/internal/runtime.iface" @"github.com/goplus/llgo/internal/runtime.MakeAnyString"([21 x i8] c"I2Int: type mismatch\00")
-  call void @abort()
+  unreachable
 }
 
 define %"github.com/goplus/llgo/internal/runtime.iface" @"github.com/goplus/llgo/internal/runtime.MakeAny"(ptr %0, ptr %1) {
@@ -267,6 +267,4 @@ _llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
   ret void
 }
 
-declare void @abort()
-
 declare void @"github.com/goplus/llgo/internal/abi.init"()

ssa/package.go

@@ -326,10 +326,6 @@ func (p Package) FuncOf(name string) Function {
 	return p.fns[name]
 }
 
-func (p Package) rtAbort() Expr {
-	return p.NewFunc("abort", types.NewSignatureType(nil, nil, nil, nil, nil, false)).Expr
-}
-
 func (p Package) rtFunc(fnName string) Expr {
 	fn := p.prog.runtime().Scope().Lookup(fnName).(*types.Func)
 	name := FullName(fn.Pkg(), fnName)

ssa/stmt_builder.go

@@ -73,8 +73,7 @@ func (b Builder) Panic(v Expr) {
 	if debugInstr {
 		log.Printf("Panic %v\n", v.impl)
 	}
-	pkg := b.fn.pkg
-	b.Call(pkg.rtAbort()) // TODO(xsw): pass v
+	b.impl.CreateUnreachable() // TODO(xsw): pass v
 }
 
 // Return emits a return instruction.