libc/glibc: use the multi-inclusion capability of the new kconfig

Now that kconfig can include a file multiple times, link the glibc/eglibc
common stuff to two .in.2 files.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Alexander BIGGA"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-07/msg00000.html"

 reporter_comment=""