Enable Getwd() in wasi and add tests

src/syscall/file_emulated.go

@@ -1,4 +1,4 @@
-// +build baremetal wasi wasm
+// +build baremetal wasm
 
 // This file emulates some file-related functions that are only available
 // under a real operating system.

src/syscall/file_hosted.go

@@ -1,4 +1,4 @@
-// +build !baremetal,!wasi,!wasm
+// +build !baremetal,!wasm
 
 // This file assumes there is a libc available that runs on a real operating
 // system.

testdata/filesystem.go

@@ -34,4 +34,12 @@ func main() {
 	}
 
 	os.Stdout.Write(data)
+
+	path, err := os.Getwd()
+	if err != nil {
+		panic(err)
+	}
+	if path == "" {
+		panic("path is empty")
+	}
 }