cmake: fixed undefined ${CMAKE_INSTALL_LIBDIR}

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8cac0a1f5ef50488ec1c180026f0620a630bc594..9f5ca4c0d115806d371c4392fb4e994bcd8034ff 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,6 +14,7 @@ add_library(utf8::cpp ALIAS utf8cpp)
 if(WIN32 AND NOT CYGWIN)
     set(DEF_INSTALL_CMAKE_DIR CMake)
 else()
+    include(GNUInstallDirs) # define CMAKE_INSTALL_*
     set(DEF_INSTALL_CMAKE_DIR ${CMAKE_INSTALL_LIBDIR}/cmake/utf8cpp)
 endif()