sci-misc/boinc: Remove xlocale.h usage, fixes bug 639108

sci-misc/boinc: Remove xlocale.h usage, fixes bug 639108

>=sys-libs/glibc-2.26 dropped xlocale.h support.

From https://sourceware.org/glibc/wiki/Release/2.26#Removal_of_.27xlocale.h.27
 > The nonstandard header xlocale.h has been removed in this release. It was
 > never intended to be included directly by programs other than glibc itself,
 > and it was a strict subset of the standard header locale.h.

This commit removes the inclusion of xlocale.h, and substitutes it with
locale.h where necessary.

Tested-by: Sven Eden <yamakuzure@gmx.net>
Bug: https://bugs.gentoo.org/639108
Closes: https://bugs.gentoo.org/639108
Package-Manager: Portage-2.3.19, Repoman-2.3.6