Make errors usable from other units. Order subarray elements correctly. Correct subarray -> pointer cast. Prevent unwrapping of catch in switch.

test/test_suite/from_docs/examples_functionpointer.c3t

@@ -0,0 +1,37 @@
+// #target: x64-darwin
+
+module demo;
+define Callback = func int(char* text, int value);
+
+func int my_callback(char* text, int value)
+{
+    return 0;
+}
+
+Callback cb = &my_callback;
+
+func void main()
+{
+    int result = cb("demo", 123);
+    // ..
+}
+
+// #expect: demo.ll
+
+define i32 @demo.my_callback(i8* %0, i32 %1) #0 {
+entry:
+  %text = alloca i8*, align 8
+  %value = alloca i32, align 4
+  store i8* %0, i8** %text, align 8
+  store i32 %1, i32* %value, align 4
+  ret i32 0
+}
+
+define void @main() #0 {
+entry:
+  %result = alloca i32, align 4
+  %0 = load i32 (i8*, i32)*, i32 (i8*, i32)** @demo.cb, align 8
+  %1 = call i32 %0(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i32 0, i32 0), i32 123)
+  store i32 %1, i32* %result, align 4
+  ret void
+}