Sema: validate function pointer alignment

test/cases/compile_errors/function_ptr_alignment.zig

@@ -0,0 +1,25 @@
+comptime {
+    var a: *align(2) @TypeOf(foo) = undefined;
+    _ = a;
+}
+fn foo() void {}
+
+comptime {
+    var a: *align(1) fn () void = undefined;
+    _ = a;
+}
+comptime {
+    var a: *align(2) fn () align(2) void = undefined;
+    _ = a;
+}
+comptime {
+    var a: *align(2) fn () void = undefined;
+    _ = a;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:19: error: function pointer alignment disagrees with function alignment
+// :16:19: error: function pointer alignment disagrees with function alignment