Both 'head -n 1' and 'sed 1q' exit after printing the first line, which closes
the pipe and kills the compiler's process leaving it no chance to clean any
temporary files it might have created (e.g. Intel compiler creates 'a.out' when
it is called with additional flags like -I, -L, etc., which is the case when
$CC/$FC is an MPI wrapper.

And make sure that the result is the same as for Fortran (FC).

The conditional indicates that FC is available and all required compiler flags
are known.

Instead of tinkering its analogue.

Thomas Jahns authored 5 years ago and Sergey Kosukhin committed 2 years ago

* Given how many lines documenting the confusing pattern and how many
  compiler warnings are eliminated by this change...

The ONLY clause works only with MPI versions that have all MPI subroutines
declared in the module. According to Thomas Jahns, this is not always the case
(see comments in #4 for more details).

This way, we avoid target-specific flags '-DUSE_MPI', which result into
target-specific rules that do not use Libtool for the compilation.

Remove declaration of the 'BUILD_C_INCLUDE' and 'BUILD_FC_INCLUDE' precious variables from the configure script since they are not used.

The shortcut for the ISO C99 test, which simplifies the implementation, is copied from PPM.