Android: <= 7 might require sys/system_properties.h

The autotools rewrite in c-ares 1.25 might have broken detection
of __system_property_get() which is needed on Android versions
prior to v8 in order to read DNS server settings.

This might fix #907
Authored-By: Brad House (@bradh352)

configure.ac

@@ -373,7 +373,7 @@ AS_HELP_STRING([--enable-libgcc],[use libgcc when linking]),
 dnl check for a few basic system headers we need.  It would be nice if we could
 dnl split these on separate lines, but for some reason autotools on Windows doesn't
 dnl allow this, even tried ending lines with a backslash.
-AC_CHECK_HEADERS([malloc.h memory.h AvailabilityMacros.h sys/types.h sys/time.h sys/select.h sys/socket.h sys/filio.h sys/ioctl.h sys/param.h sys/uio.h sys/random.h sys/event.h sys/epoll.h assert.h iphlpapi.h netioapi.h netdb.h netinet/in.h netinet6/in6.h netinet/tcp.h net/if.h ifaddrs.h fcntl.h errno.h socket.h strings.h stdbool.h time.h poll.h limits.h arpa/nameser.h arpa/nameser_compat.h arpa/inet.h ],
+AC_CHECK_HEADERS([malloc.h memory.h AvailabilityMacros.h sys/types.h sys/time.h sys/select.h sys/socket.h sys/filio.h sys/ioctl.h sys/param.h sys/uio.h sys/random.h sys/event.h sys/epoll.h assert.h iphlpapi.h netioapi.h netdb.h netinet/in.h netinet6/in6.h netinet/tcp.h net/if.h ifaddrs.h fcntl.h errno.h socket.h strings.h stdbool.h time.h poll.h limits.h arpa/nameser.h arpa/nameser_compat.h arpa/inet.h sys/system_properties.h ],
 dnl to do if not found
 [],
 dnl to do if found
@@ -488,6 +488,9 @@ cares_all_includes="
 #ifdef HAVE_RESOLV_H
 #  include <resolv.h>
 #endif
+#ifdef HAVE_SYS_SYSTEM_PROPERTIES_H
+#  include <sys/system_properties.h>
+#endif
 #ifdef HAVE_IPHLPAPI_H
 #  include <iphlpapi.h>
 #endif