meson: Don't build glsl cache_test when shader cache is disabled

v2: - Use new with_shader_cache variable instead of
      host_machine.system() == 'windows'

Reviewed-by: Eric Anholt <eric@anholt.net>

src/compiler/glsl/tests/meson.build

@@ -30,6 +30,7 @@ test(
   suite : ['compiler', 'glsl'],
 )
 
+if with_shader_cache
   test(
     'cache_test',
     executable(
@@ -42,7 +43,7 @@ test(
     ),
     suite : ['compiler', 'glsl'],
   )
-
+endif
 
 test(
   'general_ir_test',