gtk: use setlocale() for LC_MESSAGES only

gtk: use setlocale() for LC_MESSAGES only

The QEMU code is not internationalized and assumes that it runs under
the C locale, but if we use the GTK+ UI we'll end up importing the
locale settings from the environment. This can break things, such as
the JSON generator and iotest 120 in locales that use a decimal comma.

We do however have translations for a few simple strings for the GTK+
menu items, so in order to run QEMU using the C locale, and yet have a
translated UI let's use setlocale() for LC_MESSAGES only.

Cc: qemu-stable@nongnu.org
Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>