Fortran : get_environment_variable runtime error PR96486

Fortran  :  get_environment_variable runtime error PR96486

Runtime error occurs when the type of the value argument is
character(0):  "Zero-length string passed as value...".
The status argument, intent(out), will contain -1 if the value
of the environment is too large to fit in the value argument, this
is the case if the type is character(0) so there is no reason to
produce a runtime error if the value argument is zero length.

2020-08-24  Mark Eggleston  <markeggleston@gcc.gnu.org>

libgfortran/

	PR fortran/96486
	* intrinsics/env.c: If value_len is > 0 blank the string.
	Copy the result only if its length is > 0.

2020-08-24  Mark Eggleston  <markeggleston@gcc.gnu.org>

gcc/testsuite/

	PR fortran/96486
	* gfortran.dg/pr96486.f90: New test.