tor.real fails to start on macOS 10.9

While trying to test Snowflake on a macOS 10.9 system (for #26251 (moved)), I encountered a different issue: tor.real fails to start. The error is:

dyld: lazy symbol binding failed: Symbol not found: _mach_approximate_time
  Referenced from: /Users/.../Desktop/Tor/TB nightly 2018-07-18/Tor Browser.app/Contents/MacOS/Tor/tor.real
  Expected in: /usr/lib/libSystem.B.dylib

At this point I don't know if this is a core tor bug or if it is caused by something in the Tor Browser 8.x build process.