package/libzip: fix build with cmake < 3.16

Fixes:
 - http://autobuild.buildroot.org/results/7e996aebafa4c690ff130b7d18e5b09c7b255829

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/libzip/0001-Add-FindGnuTLS-cmake-from-3-17-3.patch

@@ -0,0 +1,103 @@
+From 73f6f8ebff678a0847e6b197b574082cc285b528 Mon Sep 17 00:00:00 2001
+From: Thomas Klausner <tk@giga.or.at>
+Date: Sat, 25 Jul 2020 12:03:29 +0200
+Subject: [PATCH] Add FindGnuTLS.cmake from 3.17.3.
+
+Addresses #199
+
+[Retrieved from:
+https://github.com/nih-at/libzip/commit/73f6f8ebff678a0847e6b197b574082cc285b528]
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ cmake-compat/FindGnuTLS.cmake | 82 +++++++++++++++++++++++++++++++++++
+ 1 file changed, 82 insertions(+)
+ create mode 100644 cmake-compat/FindGnuTLS.cmake
+
+diff --git a/cmake-compat/FindGnuTLS.cmake b/cmake-compat/FindGnuTLS.cmake
+new file mode 100644
+index 00000000..819f0001
+--- /dev/null
++++ b/cmake-compat/FindGnuTLS.cmake
+@@ -0,0 +1,82 @@
++# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
++# file Copyright.txt or https://cmake.org/licensing for details.
++
++#[=======================================================================[.rst:
++FindGnuTLS
++----------
++
++Find the GNU Transport Layer Security library (gnutls)
++
++IMPORTED Targets
++^^^^^^^^^^^^^^^^
++
++This module defines :prop_tgt:`IMPORTED` target ``GnuTLS::GnuTLS``, if
++gnutls has been found.
++
++Result Variables
++^^^^^^^^^^^^^^^^
++
++``GNUTLS_FOUND``
++  System has gnutls
++``GNUTLS_INCLUDE_DIR``
++  The gnutls include directory
++``GNUTLS_LIBRARIES``
++  The libraries needed to use gnutls
++``GNUTLS_DEFINITIONS``
++  Compiler switches required for using gnutls
++``GNUTLS_VERSION``
++  version of gnutls.
++#]=======================================================================]
++
++# Note that this doesn't try to find the gnutls-extra package.
++
++
++if (GNUTLS_INCLUDE_DIR AND GNUTLS_LIBRARY)
++  # in cache already
++  set(gnutls_FIND_QUIETLY TRUE)
++endif ()
++
++if (NOT WIN32)
++  # try using pkg-config to get the directories and then use these values
++  # in the find_path() and find_library() calls
++  # also fills in GNUTLS_DEFINITIONS, although that isn't normally useful
++  find_package(PkgConfig QUIET)
++  PKG_CHECK_MODULES(PC_GNUTLS QUIET gnutls)
++  set(GNUTLS_DEFINITIONS ${PC_GNUTLS_CFLAGS_OTHER})
++  set(GNUTLS_VERSION ${PC_GNUTLS_VERSION})
++  # keep for backward compatibility
++  set(GNUTLS_VERSION_STRING ${PC_GNUTLS_VERSION})
++endif ()
++
++find_path(GNUTLS_INCLUDE_DIR gnutls/gnutls.h
++  HINTS
++    ${PC_GNUTLS_INCLUDEDIR}
++    ${PC_GNUTLS_INCLUDE_DIRS}
++  )
++
++find_library(GNUTLS_LIBRARY NAMES gnutls libgnutls
++  HINTS
++    ${PC_GNUTLS_LIBDIR}
++    ${PC_GNUTLS_LIBRARY_DIRS}
++  )
++
++mark_as_advanced(GNUTLS_INCLUDE_DIR GNUTLS_LIBRARY)
++
++include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
++FIND_PACKAGE_HANDLE_STANDARD_ARGS(GnuTLS
++                                  REQUIRED_VARS GNUTLS_LIBRARY GNUTLS_INCLUDE_DIR
++                                  VERSION_VAR GNUTLS_VERSION_STRING)
++
++if(GNUTLS_FOUND)
++  set(GNUTLS_LIBRARIES    ${GNUTLS_LIBRARY})
++  set(GNUTLS_INCLUDE_DIRS ${GNUTLS_INCLUDE_DIR})
++
++  if(NOT TARGET GnuTLS::GnuTLS)
++    add_library(GnuTLS::GnuTLS UNKNOWN IMPORTED)
++    set_target_properties(GnuTLS::GnuTLS PROPERTIES
++      INTERFACE_INCLUDE_DIRECTORIES "${GNUTLS_INCLUDE_DIRS}"
++      INTERFACE_COMPILE_DEFINITIONS "${GNUTLS_DEFINITIONS}"
++      IMPORTED_LINK_INTERFACE_LANGUAGES "C"
++      IMPORTED_LOCATION "${GNUTLS_LIBRARIES}")
++  endif()
++endif()