builder: only include `os` when building `.vsh` files (#6134)

vlib/v/builder/builder.v

@@ -67,7 +67,7 @@ pub fn new_builder(pref &pref.Preferences) Builder {
 // parse all deps from already parsed files
 pub fn (mut b Builder) parse_imports() {
 	mut done_imports := []string{}
-	if b.pref.is_script {
+	if b.pref.is_vsh {
 		done_imports << 'os'
 	}
 	// TODO (joe): decide if this is correct solution.
@@ -178,7 +178,7 @@ pub fn (b &Builder) import_graph() &depgraph.DepGraph {
 			deps << 'builtin'
 			if b.pref.backend == .c {
 				// TODO JavaScript backend doesn't handle os for now
-				if b.pref.is_script && p.mod.name != 'os' {
+				if b.pref.is_vsh && p.mod.name != 'os' {
 					deps << 'os'
 				}
 			}

vlib/v/builder/compile.v

@@ -184,7 +184,7 @@ pub fn (v Builder) get_builtin_files() []string {
 			}
 			if v.pref.backend == .c {
 				// TODO JavaScript backend doesn't handle os for now
-				if v.pref.is_script && os.exists(os.join_path(location, 'os')) {
+				if v.pref.is_vsh && os.exists(os.join_path(location, 'os')) {
 					builtin_files << v.v_files_from_dir(os.join_path(location, 'os'))
 				}
 			}

vlib/v/pref/default.v

@@ -60,7 +60,8 @@ pub fn (mut p Preferences) fill_with_defaults() {
 		p.ccompiler = default_c_compiler()
 	}
 	p.is_test = p.path.ends_with('_test.v') || p.path.ends_with('.vv')
-	p.is_script = p.path.ends_with('.v') || p.path.ends_with('.vsh')
+	p.is_vsh = p.path.ends_with('.vsh')
+	p.is_script = p.is_vsh || p.path.ends_with('.v')
 	if p.third_party_option == '' {
 		p.third_party_option = p.cflags
 		$if !windows {

vlib/v/pref/pref.v

@@ -55,6 +55,7 @@ pub mut:
 	// nofmt            bool   // disable vfmt
 	is_test             bool // `v test string_test.v`
 	is_script           bool // single file mode (`v program.v`), main function can be skipped
+	is_vsh              bool // v script (`file.vsh`) file, the `os` module should be made global
 	is_livemain         bool // main program that contains live/hot code
 	is_liveshared       bool // a shared library, that will be used in a -live main program
 	is_shared           bool // an ordinary shared library, -shared, no matter if it is live or not