MDEV-13525 mtr and mysql-test-run symlinks are not installed anymore

Install mtr and mysql-test-run symlinks in case of the out-of-source
build. This was broken in c872b100

mysql-test/CMakeLists.txt

@@ -22,6 +22,7 @@ IF(NOT ${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
     ${CMAKE_CURRENT_BINARY_DIR}/mysql-test-run.pl
     @ONLY
   )
+  SET(out_of_source_build TRUE)
 ENDIF()
 IF(UNIX)
   EXECUTE_PROCESS(
@@ -32,6 +33,12 @@ IF(UNIX)
    ./mysql-test-run.pl mysql-test-run
   WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
   ) 
+  IF(INSTALL_MYSQLTESTDIR AND out_of_source_build)
+    INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/mtr
+      ${CMAKE_CURRENT_BINARY_DIR}/mysql-test-run
+      DESTINATION ${INSTALL_MYSQLTESTDIR}
+      COMPONENT Test)
+  ENDIF()
 ENDIF()
 
 IF(CMAKE_GENERATOR MATCHES "Visual Studio")