fix(util): protect std::condition_variable methods from pthread_cancel

The changes in GCC 11.x made `std::condition_variable` implementation
internals `noexcept`. `noexcept` is known to interact particularly bad
with `pthread_cancel`, i.e. `__cxxabiv1::__force_unwind` passing through
the `noexcept` call stack frame causes a `std::terminate` call and
immediate termination of the program

Digging through the GCC ML archives[1] lead me to the idea of patching
this with a few pthread_setcancelstate's. As bad as the solution is, it
seems to be the best we can do within C++17 limits and without major
rework.

[1]: https://gcc.gnu.org/legacy-ml/gcc/2017-08/msg00156.html

include/util/sleeper_thread.hpp

@@ -8,6 +8,20 @@
 
 namespace waybar::util {
 
+/**
+ * Defer pthread_cancel until the end of a current scope.
+ *
+ * Required to protect a scope where it's unsafe to raise `__forced_unwind` exception.
+ * An example of these is a call of a method marked as `noexcept`; an attempt to cancel within such
+ * a method may result in a `std::terminate` call.
+ */
+class CancellationGuard {
+  int oldstate;
+public:
+  CancellationGuard() { pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate); }
+  ~CancellationGuard() { pthread_setcancelstate(oldstate, &oldstate); }
+};
+
 class SleeperThread {
  public:
   SleeperThread() = default;
@@ -34,6 +48,7 @@ class SleeperThread {
 
   auto sleep_for(std::chrono::system_clock::duration dur) {
     std::unique_lock  lk(mutex_);
+    CancellationGuard cancel_lock;
     return condvar_.wait_for(lk, dur, [this] { return signal_ || !do_run_; });
   }
 
@@ -41,6 +56,7 @@ class SleeperThread {
       std::chrono::time_point<std::chrono::system_clock, std::chrono::system_clock::duration>
           time_point) {
     std::unique_lock  lk(mutex_);
+    CancellationGuard cancel_lock;
     return condvar_.wait_until(lk, time_point, [this] { return signal_ || !do_run_; });
   }