Implement decent kernel exceptions

[jpsamaroo]

Currently, Julia exceptions trigger an s_trap 2, which causes the wait handler to hang, and doesn't communicate any useful information about what caused the exception. This PR replaces that mechanism with a similar mechanism to the one CUDAnative uses, but with the goal to provide proper per-kernel exceptions (as opposed to throwing the exception at the next API call).

Todo:

• [x] Pass some exception info through ring buffer
• [x] Remove need for @rocprint calls to fix kernels with exceptions
• [x] Test execution control intrinsics
• [x] Test memcpy/memset intrinsics
• [x] Implement and test free for malloc'd data
• [ ] ~Actually make the ring buffer a ring buffer (currently it's a list)~
• [ ] Protect against data races (atomic load/store the kernel ID in ExceptionEntry)
• [x] De-duplicate exceptions per-kernel
• [x] Don't overallocate the copy buffer for passing exceptions
• [ ] Clean-up malloc'd data when the kernel exits by default
• [ ] Document it all!
• [ ] Test that multi-wavefront kernels error properly