libc/uClibc: force use of ctor/dtor

Although ctor/dtor do not seem strictly required, missing them proves
rather inconvenient, as ld can't link binaries.

Reported-by: John Spencer <maillist-uclibc@barfooze.de> (sh4rm4 on IRC)
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from fac4018427d2920607e8f924672458be1b366551)

 reporter_name="Nye Liu"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

 reporter_comment=""