Like others, use HAVE_ prefix and name it HAVE_LTTNG_UST to be the same
name as exported by pkg-config While at it remove wrong comment with
_HELLO_TP_H.
Support for perf api using lttng.
Some additional build tricks needed for bebop because lttng uses dl_open
which is not compatible with a static link on a different libc as used
on the bebop