oss-fuzz: Ensure a UTF8 locale is set for the samba build

oss-fuzz: Ensure a UTF8 locale is set for the samba build

This ensures that LANG=en_US.UTF8 is set, which
Samba's build system needs to operate in UTF8 mode.

The change to use flex to generate code meant that this
difference between GitLab CI and oss-fuzz was exposed.

REF: https://github.com/google/oss-fuzz/pull/4366

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed Aug 26 03:20:46 UTC 2020 on sn-devel-184