DECC$ENABLE_GETENV_CACHE

   The C RTL supplements the list of environment variables in the
   environ table with all logical names and DCL symbols available to
   the process.

   By default, whenever getenv is called for a name not in the
   environ table, an attempt is made to resolve this as a logical
   name and, if this fails, as a DCL symbol.

   With DECC$ENABLE_GETENV_CACHE enabled, once a logical name or
   DCL name has been successfully translated, its value is stored
   in a cache. When the same name is requested in a future call
   to getenv, the value is returned from the cache instead of
   reevaluating the logical name or DCL symbol.