libc/glibc: run ./configure in CONFIG_SHELL

Tremendously helps when running on at least Ubuntu, with dash as
the system shell (ie. /bin/sh points to dash).

Reported by a few people, of which:
leming, ccct and ccole 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 =