behavior: more test coverage for stage1 issues

Closes ziglang#11995
Closes ziglang#12000

Author: wooster0

test/behavior.zig

@@ -91,6 +91,8 @@ test {
     _ = @import("behavior/bugs/11213.zig");
     _ = @import("behavior/bugs/11787.zig");
     _ = @import("behavior/bugs/11816.zig");
+    _ = @import("behavior/bugs/11995.zig");
+    _ = @import("behavior/bugs/12000.zig");
     _ = @import("behavior/bugs/12003.zig");
     _ = @import("behavior/bugs/12025.zig");
     _ = @import("behavior/bugs/12033.zig");

test/behavior/bugs/11995.zig

@@ -0,0 +1,17 @@
+fn wuffs_base__make_io_buffer(arg_data: wuffs_base__slice_u8, arg_meta: wuffs_base__io_buffer_meta) callconv(.C) void {
+    _ = arg_data;
+    _ = arg_meta;
+}
+const wuffs_base__io_buffer_meta = extern struct {
+    wi: usize,
+    ri: usize,
+    pos: u64,
+    closed: bool,
+};
+const wuffs_base__slice_u8 = extern struct {
+    ptr: [*c]u8,
+    len: usize,
+};
+test {
+    _ = wuffs_base__make_io_buffer(undefined, undefined);
+}

test/behavior/bugs/12000.zig

@@ -0,0 +1,7 @@
+const T = struct {
+    next: @TypeOf(null, @as(*const T, undefined)),
+};
+
+test {
+    _ = T;
+}