Kernel/Compiler bug

[Ryan Stone]

This may not be a compiler bug.  A quick look at the esp values
provided in that backtrace shows that at least 7KB has been used on
the stack.  The stack for kernel threads is only 8KB, and a stack
overflow can cause a double fault like that.

My suspicion would be that without optimizations on clang uses a lot
more stack space and you push over the limit.  There's a kernel build
option for the stack size that you could change to confirm.  I believe
that it's called KSTACK_PAGES.  Try increasing it to 4.