libc/(e)glibc: fix extra configparms

In case ${CT_LIBC_GLIBC_CONFIGPARMS} starts with a dash, printf will try
to interpret it as an option for itself, and will invariably flail in
panic as it does not recognise any of it.

Use a more robust solution, as suggested by Cody.

Reported-by: "Roberto A. Foglietta" <roberto.foglietta@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Cody P Schafer <devel-lists@codyps.com>

 # 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 =