GNU libc cannot be compiled in the source directory. You must build it in a separate build directory. For example, if you have unpacked the glibc sources in /src/gnu/glibc-2.4, create a directory /src/gnu/glibc-build to put the object files in. This allows removing the whole build directory in case an error occurs, which is the safest way to get a fresh start and should always be done.
