Integrate and remove Clang hardening instructions
The file contrib/clang/sanitize_blacklist.txt
contains instructions on how to build Tor with AddressSanitizer using Clang. Recent changes to the build system made most of these instructions obsolete (see legacy/trac#13538 (moved), legacy/trac#18934 (moved), legacy/trac#18841 (moved)).
FWICT the only thing that is not implemented are some CFLAGS and LDFLAGS options.