interp: print LLVM instruction in traceback

The old traceback would look like this:

    # internal/godebug
    /usr/local/go/src/internal/godebug/godebug.go:101:11: interp: test
    call <2> 0 <3> 0

    traceback:
    /usr/local/go/src/internal/godebug/godebug.go:101:11:
    call <2> 0 <3> 0
    /usr/local/go/src/internal/godebug:
    call <1> 0

With this patch, it looks like this:

    # io/fs
    /usr/local/go/src/io/fs/fs.go:144:45: interp: test
      %0 = load %runtime._interface, ptr @"internal/oserror.ErrInvalid", align 8, !dbg !316

    traceback:
    /usr/local/go/src/io/fs/fs.go:144:45:
      %0 = load %runtime._interface, ptr @"internal/oserror.ErrInvalid", align 8, !dbg !316
    /usr/local/go/src/io/fs/fs.go:137:28:
      %0 = call %runtime._interface @"io/fs.errInvalid"(ptr undef), !dbg !317

For developers (like me) who are familiar with LLVM, this is probably
easier to read. For users, I'm not sure: the instructions have quite a
lot of distracting fluff in them. But at least it contains the function
names that are called (which are not currently present in the old
traceback).
...that said, having the LLVM instructions in a bug report is probably
going to be easier for people who are familar with LLVM.

interp/errors.go

@@ -60,10 +60,10 @@ func (r *runner) errorAt(inst instruction, err error) *Error {
 	pos := getPosition(inst.llvmInst)
 	return &Error{
 		ImportPath: r.pkgName,
-		Inst:       inst.String(),
+		Inst:       inst.llvmInst.String(),
 		Pos:        pos,
 		Err:        err,
-		Traceback:  []ErrorLine{{pos, inst.String()}},
+		Traceback:  []ErrorLine{{pos, inst.llvmInst.String()}},
 	}
 }
 

interp/interpreter.go

@@ -543,7 +543,7 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 					// how this function got called.
 					callErr.Traceback = append(callErr.Traceback, ErrorLine{
 						Pos:  getPosition(inst.llvmInst),
-						Inst: inst.String(),
+						Inst: inst.llvmInst.String(),
 					})
 					return nil, mem, callErr
 				}