meson: Don't build the igt audio test without gsl available.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Acked-by: Petri Latvala <petri.latvala@intel.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/tests/meson.build b/tests/meson.build
index 7383375..4dd5a9c 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -248,7 +248,7 @@
 	test_deps += libdrm_amdgpu
 endif
 
-if alsa.found()
+if alsa.found() and gsl.found()
 	test_progs += [
 		'audio',
 	]