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>
(transplanted from 30c89d1f74a4fee73517b4ed67e843be6885447e)

 This is NOT the official version of dialog.  This version has been

 significantly modified from the original.  It is for use by the Linux

 kernel configuration script.  Please do not bother Savio Lam with 

 questions about this program.