Convert C++ function doc to Doxygen style

Otherwise Doxygen won't pick it up

Author: edolstra

src/nix/develop.cc

@@ -227,11 +227,13 @@ const static std::string getEnvSh =
 #include "get-env.sh.gen.hh"
     ;
 
-/* Given an existing derivation, return the shell environment as
-   initialised by stdenv's setup script. We do this by building a
-   modified derivation with the same dependencies and nearly the same
-   initial environment variables, that just writes the resulting
-   environment to a file and exits. */
+/**
+ * Given an existing derivation, return the shell environment as
+ * initialised by stdenv's setup script. We do this by building a
+ * modified derivation with the same dependencies and nearly the same
+ * initial environment variables, that just writes the resulting
+ * environment to a file and exits.
+ */
 static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore, const StorePath & drvPath)
 {
     auto drv = evalStore->derivationFromPath(drvPath);