How to reproduce:
1. Create new empty project
2. Switch player to iOS
3. Remove or update Ads package
4. Enable Development build and Script Debugging
5. Build Unity project
6. Open project via Xcode and try to build it
Result: build fails because it is missing symbols during linking
Undefined symbols for architecture arm64:
“_mono_log_open_asl”, referenced from:
_mono_trace_set_logdest_string in libil2cpp.a(External_il2cpp_il2cpp_external_mono_mono_utils_0.o)
“_mono_log_write_asl”, referenced from:
_mono_trace_set_logdest_string in libil2cpp.a(External_il2cpp_il2cpp_external_mono_mono_utils_0.o)
“_mono_log_close_asl”, referenced from:
_mono_trace_set_logdest_string in libil2cpp.a(External_il2cpp_il2cpp_external_mono_mono_utils_0.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Reproducible: 2019.3.0a3, 2019.3.0a2
Not reproducible: 2019.3.0a1

This issue is caused by UaaL feature, which was merged to a2.

Note: On Android project builds and runs without issues