Sema: fix error notes with wrong extern type

Author: wrongnull

src/Sema.zig

@@ -25573,7 +25573,7 @@ fn explainWhyTypeIsNotExtern(
                     try mod.errNoteNonLazy(src_loc, msg, "pointer to comptime-only type '{}'", .{pointee_ty.fmt(sema.mod)});
                     try sema.explainWhyTypeIsComptime(msg, src_loc, ty);
                 }
-                try sema.explainWhyTypeIsNotExtern(msg, src_loc, pointee_ty, position);
+                try sema.explainWhyTypeIsNotExtern(msg, src_loc, pointee_ty, .other);
             }
         },
         .Void => try mod.errNoteNonLazy(src_loc, msg, "'void' is a zero bit type; for C 'void' use 'anyopaque'", .{}),

test/cases/compile_errors/extern_function_with_unspecified_calling_convention.zig

@@ -0,0 +1,14 @@
+const Foo = extern struct {
+    f: *const fn() void,
+};
+
+pub fn entry() void {
+    _ = (Foo{}).f;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:8: error: extern structs cannot contain fields of type '*const fn () void'
+// :2:8: note: extern function must specify calling convention