all: support [noreturn] fn abc() { for{} }, mark panic/1 and exit/1with it too. (#10654)

doc/docs.md

@@ -4763,6 +4763,21 @@ fn legacy_function() {}
 fn inlined_function() {
 }
 
+// This function's calls will NOT be inlined.
+[noinline]
+fn function() {
+}
+
+// This function will NOT return to its callers.
+// Such functions can be used at the end of or blocks,
+// just like exit/1 or panic/1. Such functions can not
+// have return types, and should end either in for{}, or
+// by calling other `[noreturn]` functions.
+[noreturn]
+fn forever() {
+	for {}
+}
+
 // The following struct must be allocated on the heap. Therefore, it can only be used as a
 // reference (`&Window`) or inside another reference (`&OuterStruct{ Window{...} }`).
 [heap]