Revert "[asan] Run background thread for asan only on THUMB"

This reverts commit 5c277402.

Reverting due to Windows build issue:

sanitizer_stackdepot.cpp.obj : error LNK2005: "void __cdecl __sanitizer::StackDepotStopBackgroundThread(void)" (?StackDepotStopBackgroundThread@__sanitizer@@YAXXZ) already defined in sanitizer_common_libcdep.cpp.obj
LINK : fatal error LNK1181: cannot open input file 'projects\compiler-rt\lib\asan\CMakeFiles\RTAsan_dynamic.x86_64.dir\asan_rtl_x86_64.S.obj'