fix(c/os): add missing clearenv for macOS

c/os/_os/os.c

@@ -0,0 +1,9 @@
+#include <stdlib.h>
+
+int llgo_clearenv() {
+	extern char **environ;
+	if (environ != NULL) {
+		*environ = NULL;
+	}
+	return 0;
+}

c/os/os.go

@@ -28,7 +28,8 @@ import (
 )
 
 const (
-	LLGoPackage = "decl"
+	LLGoFiles   = "_os/os.c"
+	LLGoPackage = "link"
 )
 
 const (
@@ -150,9 +151,6 @@ func Putenv(env *c.Char) c.Int
 //go:linkname Unsetenv C.unsetenv
 func Unsetenv(name *c.Char) c.Int
 
-//go:linkname Clearenv C.clearenv
-func Clearenv()
-
 // -----------------------------------------------------------------------------
 
 //go:linkname Fchdir C.fchdir

c/os/os_linux.go

@@ -0,0 +1,24 @@
+//go:build linux
+
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package os
+
+import "C"
+
+//go:linkname Clearenv C.clearenv
+func Clearenv()

c/os/os_other.go

@@ -0,0 +1,24 @@
+//go:build !linux
+
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package os
+
+import "C"
+
+//go:linkname Clearenv C.llgo_clearenv
+func Clearenv()