Add cmake check for whether setpgrp takes arguments.

FreeBSD declares setpgrp() as taking two arguments, like Linux's
setpgid(). Detect that at configure time and adjust the call in
Pageant appropriately.

cmake/cmake.h.in

@@ -43,6 +43,8 @@
 #cmakedefine01 HAVE_CLOCK_MONOTONIC
 #cmakedefine01 HAVE_CLOCK_GETTIME
 #cmakedefine01 HAVE_SO_PEERCRED
+#cmakedefine01 HAVE_NULLARY_SETPGRP
+#cmakedefine01 HAVE_BINARY_SETPGRP
 #cmakedefine01 HAVE_PANGO_FONT_FAMILY_IS_MONOSPACE
 #cmakedefine01 HAVE_PANGO_FONT_MAP_LIST_FAMILIES
 

cmake/platforms/unix.cmake

@@ -51,6 +51,21 @@ int main(int argc, char **argv) {
            cr.pid + cr.uid + cr.gid;
 }" HAVE_SO_PEERCRED)
 
+check_c_source_compiles("
+#include <sys/types.h>
+#include <unistd.h>
+
+int main(int argc, char **argv) {
+    setpgrp();
+}" HAVE_NULLARY_SETPGRP)
+check_c_source_compiles("
+#include <sys/types.h>
+#include <unistd.h>
+
+int main(int argc, char **argv) {
+    setpgrp(0, 0);
+}" HAVE_BINARY_SETPGRP)
+
 if(HAVE_GETADDRINFO AND PUTTY_IPV6)
   set(NO_IPV6 OFF)
 else()

unix/pageant.c

@@ -330,7 +330,11 @@ void pageant_fork_and_print_env(bool retain_tty)
         /* Get out of our previous process group, to avoid being
          * blasted by passing signals. But keep our controlling tty,
          * so we can keep checking to see if we still have one. */
+#if defined HAVE_NULLARY_SETPGRP
         setpgrp();
+#elif defined HAVE_BINARY_SETPGRP
+        setpgrp(0, 0);
+#endif
     } else {
         /* Do that, but also leave our entire session and detach from
          * the controlling tty (if any). */