Fortran: Remove SAVE_EXPR on lhs in assign [PR108233]

With vectorial shaped datatypes like e.g. complex numbers, fold_convert
inserts a SAVE_EXPR.  Using that on the lhs in an assignment prevented
the update of the variable, when in a coarray.

	PR fortran/108233

gcc/fortran/ChangeLog:

	* trans-expr.cc (gfc_trans_assignment_1): Remove SAVE_EXPR on lhs.

gcc/testsuite/ChangeLog:

	* gfortran.dg/coarray/complex_1.f90: New test.