* Versions 4.1 to 4.3.2 of netcdf do not provide programmatically useful
  pre-processor predicate if the pnetcdf layer is available and report
  success when the nc_create call actually failed.

* Also intercept nc__enddef for parallel access.

* This change reduces the likely-hood of encountering compiler flag
  failures due to bad interactions of libtool and compilers later
  during the build phase.

* And fallback to serial if not. Unfortunately this can only be queried at
  run-time it seems.

* And add corresponding check to test suite.

* Since write, mmap and a number of other functions are not part of
  ISO C (i.e. strictly conforming programs must not use those), we need
  to ensure the build environment provides POSIX conformance.
* This mostly prevents unrelated bug reports later on.
* From POSIX 2008, CDI unconditionally only uses getline and has a
  work-around in case that is missing.

This reverts commit de09e3fb.