libtracefs: Add -lpthread to build

In order to use pthread functions, include -lpthread to the linked
libraries to make sure that applications that include -ltracefs do not
require to have -lpthread as well, if the application is not using
pthreads.

Link: https://lore.kernel.org/linux-trace-devel/20210408205512.52c385d0@oasis.local.home

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
1 file changed