Debugging C/Mex code... but Xcode won't resolve breakpoints

I am trying to debug a .C file that is mex'd into a MATLAB project. I followed the process here:

https://www.mathworks.com/help/matlab/matlab_external/debugging-on-mac-platforms.html

but substituted in my filename. I successfully get to the line "Run Binary MEX File in MATLAB" in the referenced webpage. But, the breakpoints I set in my code (sefade_cdl_core.c, the calling MATLAB .m file is in a parent directory... I did run "mex -g sefade_cdl_core.c").... are "shadowed out"... when I hover over the shadowed breakpoint marker, I get the mesage

"XCode won't resolve at this breakpoint because it has not been resolved

Resolving it requires that:

• The line at the breakpoint has been compiled
• The compiler generates debug information that is not stripped out (check the Build Settings)
• The library for the breakpoints is loaded."

I don't know how to check the build settings, given that MATLAB runs the compiler when I run "mex". I'm not clear if this is an issue, or what the issue can be.

Please advise how I can track down/fix this problem.

Thanks!!

Tom