llvm: bring back setup_run_environment (spack#42032)

Author: haampie

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

@@ -766,6 +766,14 @@ def setup_build_environment(self, env):
                     os.symlink(bin, sym)
             env.prepend_path("PATH", self.stage.path)
 
+    def setup_run_environment(self, env):
+        if "+clang" in self.spec:
+            env.set("CC", join_path(self.spec.prefix.bin, "clang"))
+            env.set("CXX", join_path(self.spec.prefix.bin, "clang++"))
+        if "+flang" in self.spec:
+            env.set("FC", join_path(self.spec.prefix.bin, "flang"))
+            env.set("F77", join_path(self.spec.prefix.bin, "flang"))
+
     root_cmakelists_dir = "llvm"
 
     def cmake_args(self):