PROCEDURE() declares a procedure with no interface or result type. (When
used to declare a derived type component, it must also be a NOPASS
POINTER.) Document that we allow such procedures to be called as
subroutines with implicit interfaces, despite the ISO standard -- this
is a universal extension to the language.
However, no longer allow such procedure entities to be referenced as
implicitly-typed functions -- this usage is neither portable nor
well-defined, as the compilers that do allow it do not respect the
implicit typing rules established at the point of declaration.