macOS10.12/Xcode8 introduces run-time crash when building libcurl for earlier iOS versions #1069

Peter White reported the issue on the mailing list back in September. I'm filing it here so that it won't be forgotten. I've quoted a piece below.

A possible fix is to make the configure use the correct flags, as suggested by Martin Storsjö.

On macOS Sierra (v10.12) and iOS 10, the function clock_gettime has been introduced in the Darwin kernel. When building libcurl on macOS 10.12 with Xcode 8 and iOS10 SDK, the configure script will return yes for "monotonic clock_gettime" (around Line 20434 of configure).

However, when using libcurl in an application on an earlier version of iOS, this will cause a run time crash due to a missing symbol for clock_gettime.

No crash occurs on an iPhone 6 running iOS10, but on an iPad running iOS9.3.5, a crash occurs due to a missing symbol for clock_gettime.