uclibc-ng: fix parallel build issue for arm/xtensa when LOCALE support is enabled

This patch should fix any parallel build issues found
by autobuilder lately, f.e.:
http://autobuild.buildroot.net/results/43dd5c5da0d003b654fd252c989d49c2e5872827/
http://autobuild.buildroot.net/results/cfb438f933ff7385d612d65798b0b8ed833a6476/


and many more.
Will be committed upstream, if autobuilders are working.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>