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>

 reporter_name="Harold Grovesteen"

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

 reporter_comment=""