Hi,
Developers of osmo* usually don't build stuff under MacOS, so it's not officially supported.
You are hitting a MacOS specific issue most probably related to https://osmocom.org/issues/3722
Can you make sure you are building master libosmocore? (share the commit hash you are building). It should contain 2ca8cebac67cfa179af77aa8d507fd4b96b2b230 and 2bf01d439cbbf346c333043ec0c82e6d5ef62ee2.
Please share some information about your system, like MacOS version. I guess you are using MacOS 10.14.
Can you also share with us this file from your system? /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include/time.h
Please provide the information in the redmine ticket I shared above.