libc/glibc: only install start files for NPTL

Building the start files requires a shared-capable compiler, which we do
not have when the threading implementation is LinuxThreads.

So, only build the start files when the threading implementations is NPTL.

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

reporter_name="Harold Grovesteen"

reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

reporter_comment=""