atk/meson.build: replace shared_library by library
atk/meson.build: replace shared_library by library

Use library instead of shared_library to allow the user to build a
static libatk library

Fixes:
 - http://autobuild.buildroot.org/results/347a37dd2585974bdbf3bf99158e8ee9127d1202

Signed-off-by: Fabrice Fontaine <7d88633730b8b85c1516e612893df72eae9cd341@gmail.com>

GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core