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>

 # Default test suite configuration

 # Default DejaGnu configuration

 DG_TOOLNAME = gcc

 DG_TARGET_HOSTNAME = 127.0.0.1

 DG_TARGET_USERNAME = root

 # Default tests

 DG_C_TESTS = 

 DG_CPP_TESTS =