Apple doesn't use glibc.
"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.
'I have been attempting unsuccessfully to try the latest gfortran snapshot executables...The reason for the problem is that they require the bleeding-edge version of GLIBC to run:'
http://www-zeuthen.desy.de/linear_collider/cernlib/cernlib_2...
key excerpt being: 'One problem is that the functions csqrt, csqrtf, csqrtl of libm (glibc) which are used by gcc4 are still buggy for x86_64 architectures...'
Neither of these in any way imply a general dependency on glibc. On the contrary, the second one implies you'd have more luck without it, if the issue were still extant -- which it's not, the bugs were closed out six years ago.
Second: just another example (by descending order of googleableness) of the main gcc requiring glibc.
Quite possibly there is an osx (or other bsd) specific c library that can substitute for glibc, but I did not find it, and gfortran will complain without it.
'what is it that makes you think using glibc would solve a glibc problem?' Eh? I used glibc to solve a 'missing glibc' problem. I then had other problems with glibc which I attempted to solve.
The second example is, again, an issue of gcc being built against glibc. You can build it against any libc you want, but when built against glibc, the resulting binaries are obviously going to use glibc.
You appear to have a fundamental misunderstanding of the difference between the requirements of source code, and the requirements of the binaries built from them. The latter are not the same as the former, and will vary depending on how you built the source code.
And when I just built gfortran, it didn't complain about the lack of glibc at all. If yours was complaining, I think you must have configured something incorrectly, though it escapes me what that could be.