With the exception of use in three quotes as well as our inlcuded copy
of the GPL, all use of the Free Software Foundation's postal address
has been removed.
Re #320.
Use of the STDC_HEADER pre-processor macro that the autoconf macro
used to define has been removed. Conditionalized code is now used
unconditionally. This should be fine as the macro checks for ANSI
C, i.e. C89 (ISO C90), compliant headers. We already require C99.
The `#warning` directive is turned into an error by `-Werror`. The
directive triggers is guaranteed to trigger with __GNUC__ when no
parallel support is available. This would prevent strict CI builds.
Output a message with all compilers that understand the pragma. Those
that don't should ignore it, according to C99.