contrib: gnutls: disable getentropy in gnutls configure

getentropy has been introduced only in 10.12, so it is not
available on earlier osx versions. As VLC will support up to 10.7,
disable the check.

refs #18476

contrib/src/gnutls/gnutls-disable-getentropy-osx.patch

+--- gnutls/configure.ac	2016-07-05 18:34:43.000000000 +0200
++++ gnutls.new/configure.ac	2017-08-09 21:57:44.000000000 +0200
+@@ -175,6 +175,9 @@
+ 		   enable_getrandom=getrandom],
+ 		  [AC_MSG_RESULT(no)])
+ 
++if test "$have_macosx" = "yes"; then
++AC_MSG_CHECKING([for getentropy disabled for OSX])
++else
+ AC_MSG_CHECKING([for getentropy])
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([
+ 	   #include <unistd.h>],[
+@@ -184,6 +187,7 @@
+ 		   AC_DEFINE([HAVE_GETENTROPY], 1, [Enable the OpenBSD getentropy function])
+ 		   enable_getrandom=getentropy],
+ 		  [AC_MSG_RESULT(no)])
++fi
+ 
+ dnl Try the hooks.m4
+ LIBGNUTLS_HOOKS

contrib/src/gnutls/rules.mak

@@ -37,6 +37,7 @@ endif
 	$(APPLY) $(SRC)/gnutls/mac-keychain-lookup.patch
 ifdef HAVE_MACOSX
 	$(APPLY) $(SRC)/gnutls/gnutls-pkgconfig-osx.patch
+	$(APPLY) $(SRC)/gnutls/gnutls-disable-getentropy-osx.patch
 endif
 	$(APPLY) $(SRC)/gnutls/gnutls-libidn.patch
 	$(call pkg_static,"lib/gnutls.pc.in")