Fortran: Fix host associated PDT entity initialization [PR99307].

2021-04-20  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/100110
	* trans-decl.c (gfc_get_symbol_decl): Replace test for host
	association with a check that the current and symbol namespaces
	are the same.

gcc/testsuite/
	PR fortran/100110
	* gfortran.dg/pdt_31.f03: New test.
	* gfortran.dg/pdt_26.f03: Reduce 'builtin_malloc' count from 9
	to 8.