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

@@ -30,7 +30,8 @@ test(
   suite : ['compiler', 'glsl'],
 )
 
-test(
+if with_shader_cache
+  test(
     'cache_test',
     executable(
       'cache_test',
@@ -41,8 +42,8 @@ test(
       dependencies : [dep_clock, dep_thread],
     ),
     suite : ['compiler', 'glsl'],
-)
+  )
-
+endif
 
 test(
   'general_ir_test',