"thread::details" class must be friend of "thread::id" class so "thread::details::get_current_thread_id()" can constructor a "thread::id" with the current thread ID as parameter.
"thread::details" class must be friend of "thread::id" class so "thread::details::get_current_thread_id()" can constructor a "thread::id" with the current thread ID as parameter.

Signed-off-by: David Capello <09b3026e571b53d34b9bb05309b01d3b4f4663b2@gmail.com>

dacap/cpp-utils