The code generated for Thumb and Thumb2 targets has different handling
for abort(). Because abort() is "noreturn", it doesn't need to preserve
the callee-save registers. The Thumb2 version trashes LR and makes it
impossible to figure out who called abort().
This inserts a trivial stub function; net effect is stack traces are
reasonable after an abort().
For bug 2191452.
Eclair branch Dr. No approved by: hiroshi
the issue here is that abort() can be called from anywhere, in particular
from malloc or free. When we try to use the debug_log functions, these
can end up calling into some code (like malloc/free) that called abort()
in the first place and end up in an infinite recursion loop.
