Use GNUInstallDirs CMAKE_INSTALL_INCLUDEDDIR path for headers installation

Author: Begasus

include/CMakeLists.txt

@@ -5,13 +5,13 @@ if(INSTALL_MBEDTLS_HEADERS)
     file(GLOB headers "mbedtls/*.h")
 
     install(FILES ${headers}
-        DESTINATION include/mbedtls
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/mbedtls
         PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ)
 
     file(GLOB private_headers "mbedtls/private/*.h")
 
     install(FILES ${private_headers}
-        DESTINATION include/mbedtls/private
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/mbedtls/private
         PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ)
 endif(INSTALL_MBEDTLS_HEADERS)