[flang] Propagate the BIND(C) attribute into procedures from their in… (#93994)

…terfaces

In "PROCEDURE(iface) :: proc", if "iface" has the BIND(C) attribute,
then so should proc, as if the declaration had been "PROCEDURE(iface),
BIND(C) :: proc". This had been working in name resolution only in cases
where "iface" had been declared before "proc".

Note that if "iface" is declared with an empty binding name
("BIND(C,NAME='')"), "proc" does not inherit that property. Use an
explicit "BIND(C,NAME='')" on the "PROCEDURE" statement for that.

This behavior is not clearly defined in the standard, but seems to match
what some other Fortran compilers do.