getrandom() may require sys/random.h on some systems

There is a reported build issue where getrandom() is detected
but compile fails due to a missing prototype. This commit attempts
to resolve that issue.

Fixes Bug: #665
Fix By: Brad House (@bradh352)

CMakeLists.txt

@@ -225,6 +225,7 @@ CHECK_INCLUDE_FILES (sys/select.h          HAVE_SYS_SELECT_H)
 CHECK_INCLUDE_FILES (sys/stat.h            HAVE_SYS_STAT_H)
 CHECK_INCLUDE_FILES (sys/time.h            HAVE_SYS_TIME_H)
 CHECK_INCLUDE_FILES (sys/uio.h             HAVE_SYS_UIO_H)
+CHECK_INCLUDE_FILES (sys/random.h          HAVE_SYS_RANDOM_H)
 CHECK_INCLUDE_FILES (ifaddrs.h             HAVE_IFADDRS_H)
 CHECK_INCLUDE_FILES (time.h                HAVE_TIME_H)
 CHECK_INCLUDE_FILES (dlfcn.h               HAVE_DLFCN_H)
@@ -323,6 +324,7 @@ CARES_EXTRAINCLUDE_IFSET (HAVE_SYS_SOCKIO_H	sys/sockio.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_SYS_TIME_H     sys/time.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_SYS_STAT_H     sys/stat.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_SYS_UIO_H      sys/uio.h)
+CARES_EXTRAINCLUDE_IFSET (HAVE_SYS_RANDOM_H   sys/random.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_TIME_H         time.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_FCNTL_H        fcntl.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_UNISTD_H       unistd.h)

configure.ac

@@ -574,6 +574,7 @@ AC_CHECK_HEADERS(
        sys/ioctl.h \
        sys/param.h \
        sys/uio.h \
+       sys/random.h \
        assert.h \
        iphlpapi.h \
        netioapi.h \

src/lib/ares_config.h.cmake

@@ -320,6 +320,9 @@
 /* Define to 1 if you have the <sys/param.h> header file. */
 #cmakedefine HAVE_SYS_PARAM_H
 
+/* Define to 1 if you have the <sys/random.h> header file. */
+#cmakedefine HAVE_SYS_RANDOM_H
+
 /* Define to 1 if you have the <sys/select.h> header file. */
 #cmakedefine HAVE_SYS_SELECT_H
 

src/lib/ares_rand.c

@@ -28,6 +28,9 @@
 #include "ares.h"
 #include "ares_private.h"
 #include <stdlib.h>
+#ifdef HAVE_SYS_RANDOM_H
+#  include <sys/random.h>
+#endif
 
 
 typedef enum {