Fix fiber abortion.

When aborting a fiber, we need to activate it once more, to then leave
it for good by raising an `AbortException. Problem was that that
exception ended up being caught by user code because it was derived
from `std::exception`. This change removes the base class so that the
exception is guaranteed to go back to the managing fiber code, where
we just ignore it.

(cherry picked from commit 193c335)

Author: rsmmr

hilti/runtime/src/fiber.cc

@@ -230,8 +230,11 @@ detail::Fiber::Fiber(Type type) : _type(type), _fiber(std::make_unique<::Fiber>(
     };
 }
 
-HILTI_EXCEPTION(AbortException, RuntimeError);
-AbortException::~AbortException() = default;
+// Exception raised by a fiber resuming operation in case it has been aborted
+// in the meantime. This must not be derived from `std::exception` to guarantee
+// that it will bubble back up to the fiber code, without being caught by any
+// intermediary catch handlers.
+struct AbortException {};
 
 detail::Fiber::~Fiber() {
 #ifndef NDEBUG
@@ -502,7 +505,7 @@ void detail::Fiber::yield() {
     _yield("yield");
 
     if ( _state == State::Aborting )
-        throw AbortException("processing aborted for input");
+        throw AbortException();
 }
 
 void detail::Fiber::resume() {
@@ -517,7 +520,12 @@ void detail::Fiber::abort() {
     if ( ! context::detail::get(true) )
         return;
 
-    run();
+    try {
+        run();
+    } catch ( const AbortException& ) {
+        // Exception is expected here when the fiber realizes it has been
+        // aborted.
+    }
 }
 
 std::unique_ptr<detail::Fiber> detail::Fiber::create() {

tests/Baseline/spicy.types.sink.reassembler.wrong-init-seq/output

@@ -1,2 +1,2 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
-[error] terminating with uncaught exception of type spicy::rt::SinkError: sink cannot update initial sequence number after activity has already been seen (<...>/wrong-init-seq.spicy:20:19-38:1)
+[error] terminating with uncaught exception of type spicy::rt::SinkError: sink cannot update initial sequence number after activity has already been seen (<...>/wrong-init-seq.spicy:14:9-14:50)