glibc 2.3 not binary compatible with glibc-2.2.5

[Roland McGrath]

If __builtin_frame_address (0) is supposed to work in a leaf function when
compiled with -fomit-frame-pointer, then it's a GCC bug that it doesn't.
The documentation I have seen is not explicitly clear about it, but it is
reasonable enough if __builtin_frame_address is just not supposed to work
with -fomit-frame-pointer.  In that case, it's a libc bug.