Add comments about using debug_assert

Author: ChrisDenton

library/std/src/sys/pal/windows/stack_overflow.rs

@@ -6,6 +6,8 @@ use crate::thread;
 /// Reserve stack space for use in stack overflow exceptions.
 pub unsafe fn reserve_stack() {
     let result = c::SetThreadStackGuarantee(&mut 0x5000);
+    // Reserving stack space is not critical so we allow it to fail in the released build of libstd.
+    // We still use debug assert here so that CI will test that we haven't made a mistake calling the function.
     debug_assert_ne!(result, 0, "failed to reserve stack space for exception handling");
 }
 
@@ -26,6 +28,8 @@ unsafe extern "system" fn vectored_handler(ExceptionInfo: *mut c::EXCEPTION_POIN
 
 pub unsafe fn init() {
     let result = c::AddVectoredExceptionHandler(0, Some(vectored_handler));
+    // Similar to the above, adding the stack overflow handler is allowed to fail
+    // but a debug assert is used so CI will still test that it normally works.
     debug_assert!(!result.is_null(), "failed to install exception handler");
     // Set the thread stack guarantee for the main thread.
     reserve_stack();