Fix pthread detection for regress tests on Android

Fixes: #1403

CMakeLists.txt

@@ -556,6 +556,7 @@ else()
     endif()
 endif()
 
+set(PTHREADS_AVAILABLE OFF)
 if (NOT EVENT__DISABLE_THREAD_SUPPORT)
     if (WIN32)
         list(APPEND SRC_CORE evthread_win32.c)
@@ -564,12 +565,14 @@ if (NOT EVENT__DISABLE_THREAD_SUPPORT)
         set(EVENT__HAVE_PTHREADS 1)
         CHECK_TYPE_SIZE(pthread_t EVENT__SIZEOF_PTHREAD_T)
         list(APPEND SYMBOLS_TO_CHECK pthread_mutexattr_setprotocol)
+        set(PTHREADS_AVAILABLE ON)
     else()
         find_package(Threads REQUIRED)
         if (NOT CMAKE_USE_PTHREADS_INIT)
             message(FATAL_ERROR
                     "Failed to find Pthreads, set EVENT__DISABLE_THREAD_SUPPORT to disable")
         endif()
+        set(PTHREADS_AVAILABLE ON)
 
         set(EVENT__HAVE_PTHREADS 1)
         list(APPEND LIB_APPS ${CMAKE_THREAD_LIBS_INIT})
@@ -1294,7 +1297,7 @@ if (NOT EVENT__DISABLE_TESTS)
             if (NOT EVENT__DISABLE_MBEDTLS)
                 target_link_libraries(regress event_mbedtls)
             endif()
-            if (CMAKE_USE_PTHREADS_INIT)
+            if (PTHREADS_AVAILABLE)
                 target_link_libraries(regress event_pthreads)
             endif()
         else()