perf tools: Add doc about how to build perf with Asan and UBSan

AddressSanitizer (or ASan) and UndefinedBehaviorSanitizer (or UBSan) are
very useful tools to detect program bugs:

 - AddressSanitizer (or ASan) is a GCC feature that detects memory
   corruption bugs such as buffer overflows and memory leaks.

 - UndefinedBehaviorSanitizer (or UBSan) is a fast undefined behavior
   detector supported by GCC. UBSan detects undefined behaviors of programs
   at runtime.

This patch adds a document about how to use them on perf. Later patches will fix
some of the issues disclosed by them.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20190316080556.3075-2-changbin.du@gmail.com


[ Make some changes based on comments made by Jiri Olsa ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>