js: implement more functions for JS backend (#12167)

vlib/v/pref/os.v

@@ -112,5 +112,18 @@ pub fn get_host_os() OS {
 	$if haiku {
 		return .haiku
 	}
+	$if js_node {
+		return .js_node
+	}
+	$if js_freestanding {
+		return .js_freestanding
+	}
+
+	$if js_browser {
+		return .js_browser
+	}
+	$if js {
+		return .js_node
+	}
 	panic('unknown host OS')
 }

vlib/v/util/util.v

@@ -171,6 +171,9 @@ pub fn launch_tool(is_verbose bool, tool_name string, args []string) {
 	}
 	$if windows {
 		exit(os.system('"$tool_exe" $tool_args'))
+	} $else $if js {
+		// no way to implement os.execvp in JS backend
+		exit(os.system('$tool_exe $tool_args'))
 	} $else {
 		os.execvp(tool_exe, args) or { panic(err) }
 	}