meson: define SETPGRP_VOID

All current systems have a setpgrp whose signature conforms to Posix.

We need to set this to use the correct implementation internally
but we don't need to check for it.

Signed-off-by: Matt Jolly <kangie@gentoo.org>

meson.build

@@ -176,6 +176,14 @@ foreach f, v : functions
     endif
 endforeach
 
+# SETPGRP_VOID is obsolete
+# All current systems have a setpgrp whose signature conforms to Posix.
+# We need to set this to use the correct implementation internally
+# but we don't need to check for it.
+if conf.has('HAVE_SETPGRP')
+    conf.set('SETPGRP_VOID', 1)
+endif
+
 # Dependencies.
 all_found_deps = []