update std lib to use error type and global variables

example/multiple_files/foo.zig

@@ -3,7 +3,7 @@ import "std.zig";
 // purposefully conflicting function with main.zig
 // but it's private so it should be OK
 fn private_function() => {
-    print_str("OK 1\n");
+    stdout.printf("OK 1\n");
 }
 
 pub fn print_text() => {

example/multiple_files/main.zig

@@ -5,7 +5,7 @@ import "foo.zig";
 
 pub fn main(args: [][]u8) i32 => {
     private_function();
-    print_str("OK 2\n");
+    stdout.printf("OK 2\n");
     return 0;
 }