upcxx %oneapi@2025: cxxflags add -Wno-error=missing-template-arg-list…

…-after-template-kw (spack#47503)

var/spack/repos/builtin/packages/upcxx/package.py

@@ -164,7 +164,11 @@ class Upcxx(Package, CudaPackage, ROCmPackage):
     depends_on("oneapi-level-zero@1.8.0:", when="+level_zero")
 
     # All flags should be passed to the build-env in autoconf-like vars
-    flag_handler = env_flags
+    def flag_handler(self, name, flags):
+        if name == "cxxflags":
+            if self.spec.satisfies("%oneapi@2025:"):
+                flags.append("-Wno-error=missing-template-arg-list-after-template-kw")
+        return (flags, None, None)
 
     def set_variables(self, env):
         env.set("UPCXX_INSTALL", self.prefix)