sync code with last improvements from OpenBSD

lib/mesa/.gitlab-ci/container/build-skqp_is_clang.py.patch

@@ -0,0 +1,13 @@
+diff --git a/gn/BUILDCONFIG.gn b/gn/BUILDCONFIG.gn
+index 454334a..1797594 100644
+--- a/gn/BUILDCONFIG.gn
++++ b/gn/BUILDCONFIG.gn
+@@ -80,7 +80,7 @@ if (current_cpu == "") {
+ is_clang = is_android || is_ios || is_mac ||
+            (cc == "clang" && cxx == "clang++") || clang_win != ""
+ if (!is_clang && !is_win) {
+-  is_clang = exec_script("gn/is_clang.py",
++  is_clang = exec_script("//gn/is_clang.py",
+                          [
+                            cc,
+                            cxx,