intel/compiler: add cpp_std=c++17 when building tests

Otherwise build fails:

"../src/intel/compiler/brw_private.h:40:4: note:
 ‘std::variant’ is only available from C++17 onwards"

Fixes: 6c194ddd18 ("intel/compiler: Prepare SIMD selection helpers to handle different prog_datas")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20725>
(cherry picked from commit 53de48f1c4)

.pick_status.json

@@ -49,7 +49,7 @@
         "description": "intel/compiler: add cpp_std=c++17 when building tests",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "6c194ddd18f24a2fe995aa6b09c8d5d6d2c97d34"
     },

src/intel/compiler/meson.build

@@ -208,6 +208,7 @@ if with_tests
       link_with : [
         libintel_compiler, libintel_common, libintel_dev, libisl,
       ],
+      override_options: ['cpp_std=c++17'],
       dependencies : [idep_gtest, idep_nir, idep_mesautil],
     ),
     suite : ['intel'],