ARM thumb/thumb2 frame pointer is inconsistent on GCC and Clang 
and fast-unwider is also unreliable with mixing arm and thumb code .
The fast unwinder ARM hacks to probe and compare the frame-pointer
in different stack layout position works reliable only on a system where
all the libraries are built in arm mode (either with gcc or clang).
However when mixing objects built with different abi mode the
fast unwinder is still problematic. The quarantine_size_mb.cpp
still fails on ARM on system with libraries built with thumb (Ubuntu
bionic for instance) so make is pass clean this patch forces it to
use the slow unwinder is to avoid a leak warning triggered by the
helper quarantine thread creation (the allocation is done by glibc
pthread_create). Without proper stack frame information libsanitizer
can not apply the expected suppresion in this case.
This should fix BZ#44158, however the leak sanitizier is still
unreliable on most distros where the system compiler defaults to