fork() semantics can be problematic. Most unix style OS'es have
posix_spawn which can be used to replace fork + exec in many cases.
For more information see
e.g. https://www.microsoft.com/en-us/research/uploads/prod/2019/04/fork-hotos19.pdf
This replaces the one use of fork in libgfortran with posix_spawn.
2019-05-17 Janne Blomqvist <jb@gcc.gnu.org>
PR libfortran/90038
* configure.ac (AC_CHECK_FUNCS_ONCE): Check for posix_spawn.
* intrinsics/execute_command_line (execute_command_line): Use
posix_spawn.
* Makefile.in: Regenerated.
* config.h.in: Regenerated.
* configure: Regenerated.
Regtested on x86_64-pc-linux-gnu.
From-SVN: r271340
f888603842