toolchain/uClibc: fix default configs with respect to bug #5018

Switch from the strict UCLIBC_HAS_CTYPE_ENFORCED=y to the less
restrictive UCLIBC_HAS_CTYPE_CHECKED=y since it breaks dialog under
certain circumstances (bug #5018).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>