* This should reduce unnecessary recompilations after e.g. re-running
  configure or config.status.

* These may occur during mpich 4.1.x startup.

* The C compiler selection got some major updates in both releases.

* Cray ftn version 10.0.2 also runs into this problem in debug mode.
  It appears the incorrect preprocessor macro recently fixed only
  went unnoticed because the bug disappears when the optimizer kicks
  in.
* debug mode here referring to -O0 -g in FCFLAGS.

* Either initialize padding bytes on x86 and x86_64 explicitly or by
  declaring variables in text segment. Otherwise valgrind reports use
  of uninitialized memory in the memcmp test.

* This way, source files for overrides need only be specified in configure and
  no longer also use per-file special rules in Makefile.

* The issue remains in version 3.4.3.