Make parking_control (etc) use vtables (#6275)

* Make parking_control (etc) use vtables

This class hierarchy is clearly best modeled with virtual methods (rather than fn ptrs), but was not; we *think* this was due to COMDAT issues that have been resolved by other means. I refactored this to use virtual methods instead (and removed the unused unpark_all function); it seems to work locally.

* Add -fno-rtti to runtime compile flags (needed to allow vtables in runtime code)

* make all overrides 'final'

* Make virtual methods protected

* Make structs final too

* pacify clang-tidy

Makefile

@@ -989,7 +989,9 @@ RUNTIME_TRIPLE_WIN_GENERIC_64 = "le64-unknown-windows-unknown"
 
 # `-fno-threadsafe-statics` is very important here (note that it allows us to use a 'modern' C++
 # standard but still skip threadsafe guards for static initialization in our runtime code)
-RUNTIME_CXX_FLAGS = -std=c++17 -O3 -fno-vectorize -ffreestanding -fno-blocks -fno-exceptions -fno-unwind-tables -fno-threadsafe-statics
+#
+# `-fno-rtti` is necessary to allow us to use classes with virtual functions in the runtime code
+RUNTIME_CXX_FLAGS = -std=c++17 -O3 -fno-vectorize -ffreestanding -fno-blocks -fno-exceptions -fno-unwind-tables -fno-threadsafe-statics -fno-rtti
 
 $(BUILD_DIR)/initmod.windows_%_x86_32.ll: $(SRC_DIR)/runtime/windows_%_x86.cpp $(BUILD_DIR)/clang_ok
 	@mkdir -p $(@D)

src/runtime/CMakeLists.txt

@@ -152,6 +152,8 @@ set(RUNTIME_CXX_FLAGS
     -fno-vectorize
     # Note: we don't want static locals to get thread synchronization stuff.
     -fno-threadsafe-statics
+    # Necessary for using virtual functions in the runtime code.
+    -fno-rtti
     -Wall
     -Wcast-qual
     -Werror