support getrandom syscall on non-linux

At least FreeBSD and NetBSD also implement getrandom using the same
semantics as Linux >= 3.17. They don't define any of it it in
linux/random.h, however. They do define all the necessary bits in
sys/random.h. glibc >= 2.25 also defines it there as well as in
linux/random.h. Simply use sys/random.h when checking for its existence.

Author: dankm

Modules/posixmodule.c

@@ -148,6 +148,9 @@
 #  include <sys/sysctl.h>
 #endif
 
+#ifdef HAVE_SYS_RANDOM_H
+#  include <sys/random.h>       // GRND_RANDOM on !Linux
+#endif
 #ifdef HAVE_LINUX_RANDOM_H
 #  include <linux/random.h>       // GRND_RANDOM
 #endif

configure

@@ -7377,7 +7377,7 @@ AC_LINK_IFELSE(
     #include <stddef.h>
     #include <unistd.h>
     #include <sys/syscall.h>
-    #include <linux/random.h>
+    #include <sys/random.h>
 
     int main(void) {
         char buffer[1];