interface: add sample filesystem interface

interface/CMakeLists.txt

@@ -0,0 +1,7 @@
+file(GLOB if_files *.if)
+
+foreach (file ${if_files})
+	get_filename_component(name ${file} NAME_WLE)
+	add_interface(NAME ${name} PATH ${file} PARENT_DIR rosetta)
+	sysroot_add_interface(NAME ${name} DEST_DIR /usr/include)
+endforeach (file)

interface/fs.if

@@ -0,0 +1,4 @@
+interface fs {
+	msg open(string path, int flags) -> (int err);
+	msg uppercase(string old) -> (string new);
+}