Backports for tsfn

[mhdawson]

Need to backport to 8.x and 10.x and make non experimental to help adoption.

[mhdawson]

Gabriel - already in as experimental in 10.X

Steps:

1. Make non-experimental in master
2. roll back to 10.x and 8.x

Gabriel will get the ball rolling.

[gabrielschulhof]

v10.x backport: nodejs/node#25633
v8.x backport: nodejs/node#25648

[mhdawson]

From the meeting today sounds like there is a problem with FreeBSD 10 in the 10.x staging and release branches. Believe its the same problem that I refereed to in nodejs/node#25574.

[gabrielschulhof]

The commit on v10.x-staging that seems to have introduced the failure to compile on FreeBSD 10 is this: nodejs/node@acf7e7d

[gabrielschulhof]

These backports have now landed.