cmake: whoops, Sam and I both fixed this bug at the same time. :)

cmake/sdlchecks.cmake

@@ -862,8 +862,6 @@ macro(CheckPTHREAD)
     elseif(LINUX)
       set(PTHREAD_CFLAGS "-D_REENTRANT")
       set(PTHREAD_LDFLAGS "-pthread")
-    elseif(ANDROID)
-      # pthreads are builtin
     elseif(BSDI)
       set(PTHREAD_CFLAGS "-D_REENTRANT -D_THREAD_SAFE")
       set(PTHREAD_LDFLAGS "")