Fix aliased string move interface

[perazz]

Fixes #744 (previous fix: #736)

The following line is causing a segfault on macOS, gfortran 13.2.0, hence failed test:

stdlib/test/string/test_string_intrinsic.f90

Line 717 in b8fbb3c

call move(from_string, from_string)

I believe this line is invalid Fortran because it violates the no-alising rule: two dummy arguments passed by reference cannot point to the same address. So probably, gfortran optimizes out the temporary variable which then causes trouble.

My proposed solution is to check the address first, and avoid the dangerous operation if the variable is the same.

cc: @Pranavchiku @wpbonelli @jvdp1 @awvwgk

[awvwgk]

That's a great usage of pointer association and targets. I think we can work with that.

[jvdp1]

Nice solution! Thank you @perazz

[perazz]

Thank you Sebastian and Jeremie, I'm going to wait another few days, then merge if there are no more comments.