folly | Fix folly::setThreadName, folly::getThreadName on iOS/watchOS/tvOS.
folly | Fix folly::setThreadName, folly::getThreadName on iOS/watchOS/tvOS.

Summary:
According to headers, `pthread_getname_np` and `pthread_setname_np` are available since iOS 3.2 and macOS 10.6.
However, guarding just on min macOS version isn't going to work for iOS/watchOS/tvOS, because it's very rarely defined.
So add another case for when `__IPHONE_OS_VERSION_MIN_REQUIRED` is defined and is above iOS 3.2, which will also make watchOS and tvOS work.

Reviewed By: yfeldblum

Differential Revision: D7648204

fbshipit-source-id: 1e608cdad3f39242eff79fbb6da8e560eeee720a

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