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* Unfortunately, the PGI compiler generates incorrect code here when
  optimizing and the kinds do not match.

* This prevents warnings for superfluous imports.

* Also remove flag that configure can deduce by itself.

* This should be abandoned once a newer gfortran can be made
  to not generate a warning for this.

* The previous implementation treated the input path as a regular
  expression.

* Without this, gfortran 9 will complain.
* And, of course, pgfortran does not allow iand in initialization
  expressions.

* The previous version practically always used the xt_slice_c_loc
  fallback, when only certain versions of gcc needed to be
  avoided.

* This placates g95. I know.