Kernel: KUBSAN! (Kernel Undefined Behavior SANitizer) :^)

We now build the kernel with partial UBSAN support.
The following -fsanitize sub-options are enabled:

* nonnull-attribute
* bool

If the kernel detects UB at runtime, it will now print a debug message
with a stack trace. This is very cool! I'm leaving it on by default for
now, but we'll probably have to re-evaluate this as more options are
enabled and slowdown increases.

Kernel/CMakeLists.txt

@@ -197,6 +197,7 @@ set(KERNEL_SOURCES
     Time/RTC.cpp
     Time/TimeManagement.cpp
     TimerQueue.cpp
+    UBSanitizer.cpp
     UserOrKernelBuffer.cpp
     VM/AnonymousVMObject.cpp
     VM/ContiguousVMObject.cpp
@@ -269,6 +270,7 @@ set(SOURCES
     ${C_SOURCES}
 )
 
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=nonnull-attribute,bool")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unknown-warning-option -DKERNEL")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pie -fPIE -fno-rtti -ffreestanding -fbuiltin")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mno-80387 -mno-mmx -mno-sse -mno-sse2")