allow building on Tinygo

This commit adds package internal/tinygostub that contains
stubs for some of the standard library functions that are not
available in Tinygo.

This allows most of the module to be built with Tinygo.

internal/tinygostub/samefile.go

@@ -0,0 +1,10 @@
+//go:build !(tinygo && wasm)
+
+package tinygostub
+
+import "os"
+
+// SameFile calls [os.SameFile].
+func SameFile(fi1, fi2 os.FileInfo) bool {
+	return os.SameFile(fi1, fi2)
+}

internal/tinygostub/samefile_tinygo_wasm.go

@@ -0,0 +1,10 @@
+//go:build tinygo && wasm
+
+package tinygostub
+
+import "os"
+
+// SameFile returns false.
+func SameFile(fi1, fi2 os.FileInfo) bool {
+	return false
+}

interp/test.go

@@ -13,6 +13,7 @@ import (
 	"golang.org/x/term"
 
 	"mvdan.cc/sh/v3/expand"
+	"mvdan.cc/sh/v3/internal/tinygostub"
 	"mvdan.cc/sh/v3/syntax"
 )
 
@@ -88,7 +89,7 @@ func (r *Runner) binTest(ctx context.Context, op syntax.BinTestOperator, x, y st
 		if err1 != nil || err2 != nil {
 			return false
 		}
-		return os.SameFile(info1, info2)
+		return tinygostub.SameFile(info1, info2)
 	case syntax.TsEql:
 		return atoi(x) == atoi(y)
 	case syntax.TsNeq: