meson: bump required version to 0.46

0.45 has a few annoying bugs (like the one in !358 [1]), and 0.46 is
well over a year old by now, so let's move to it.

[1] https://gitlab.freedesktop.org/mesa/mesa/merge_requests/358

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
1 file changed