Export a zstd::libzstd target if only static or dynamic linkage is specified.

build/cmake/zstdConfig.cmake.in

@@ -0,0 +1,16 @@
+@PACKAGE_INIT@
+
+include(CMakeFindDependencyMacro)
+if(@ZSTD_MULTITHREAD_SUPPORT@ AND "@UNIX@")
+  find_dependency(Threads)
+endif()
+
+include("${CMAKE_CURRENT_LIST_DIR}/zstdTargets.cmake")
+
+if(@ZSTD_BUILD_SHARED@ AND NOT @ZSTD_BUILD_STATIC@)
+  add_library(zstd::libzstd ALIAS zstd::libzstd_shared)
+elseif(NOT @ZSTD_BUILD_SHARED@ AND @ZSTD_BUILD_STATIC@)
+  add_library(zstd::libzstd ALIAS zstd::libzstd_static)
+endif()
+
+check_required_components("zstd")