Fix CMake 4.1 warning "ELSEIF called with no arguments"

Also remove HAVE_THREADS CMake variable setting, it is not used anywhere.

Author: vaintroub

CMakeLists.txt

@@ -287,11 +287,8 @@ ADD_DEFINITIONS(-DMARIADB_SYSTEM_TYPE="${CMAKE_SYSTEM_NAME}")
 ADD_DEFINITIONS(-DMARIADB_MACHINE_TYPE="${CMAKE_SYSTEM_PROCESSOR}")
 
 IF(WIN32)
-  SET(HAVE_THREADS 1)
   ADD_DEFINITIONS(-DHAVE_DLOPEN)
   ADD_DEFINITIONS(-D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE)
-ELSEIF()
-  SET(HAVE_THREADS ${CMAKE_USE_PTHREADS})
 ENDIF()
 
 IF(NOT DEFAULT_CHARSET)