Fix PR 118884, Lapack build failure.

Fix PR 118884, Lapack build failure.

The fix for PR 118845 introduced new checks, which in turn exposed
a case where the typespec information on a symbol generated symbol
was not set.  This led to an apparent type of BT_UNKNOWN, and hence
an error.  Fixed as obvoius and simple.

gcc/fortran/ChangeLog:

	* frontend-passes.cc (check_externals_procedure): Copy
	typespec from old to new symbol.

gcc/testsuite/ChangeLog:

	* gfortran.dg/interface_54.f90: New test.