I needed it for my gcc and gfortran install. I am not sure whether osx uses glibc for xcode. Somehow despite removing and replacing everything related to glibc, it was still broken. Never did figure it out.
Sure, the problem was installing gfortran, which (as I recall) requires the real gcc. I suspect (though I never did figure out what exactly was wrong) that some sort of a library conflict with xcode's gcc was responsible. As this package is still not the real gcc (they don't want gpl v3 I believe) anyone who wants eg. gfortran will still need a separate installation.
gcc and glibc are different things, and gcc does not require glibc. I don't know that glibc even runs on OS X/Darwin, it would seem strange for any time to be invested in such an endeavour.
I can't find any evidence of that. The gfortran 4.3 release notes strongly imply it doesn't:
"Support for backtraces on glibc-based systems via the -fbacktrace option is now implemented. On all systems, a coredump can be generated for errors in the run-time library using `-fdump-core`."
The GCC suite has a pretty clear history of not being dependent on glibc, and some searching brings up no mention of it requiring glibc, and a few mentions of people clearly building it without glibc.