Enable libutil by default for uclibc 0.9.31

Closes #1591

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/uClibc/uClibc-0.9.31.config

@@ -94,7 +94,7 @@ UCLIBC_HAS_PTY=y
 ASSUME_DEVPTS=y
 UNIX98PTY_ONLY=y
 # UCLIBC_HAS_GETPT is not set
-# UCLIBC_HAS_LIBUTIL is not set
+UCLIBC_HAS_LIBUTIL=y
 UCLIBC_HAS_TM_EXTENSIONS=y
 UCLIBC_HAS_TZ_CACHING=y
 UCLIBC_HAS_TZ_FILE=y