FindThreads: Revert libc symbol check to pthread_create

Since commit e9a1ddc594 (FindThreads: Replace the pthread symbol
checking in libc., 2018-11-18, v3.14.0-rc1~292^2) we check libc for
`pthread_kill` instead of `pthread_create`.  However, on FreeBSD
`pthread_kill` is in libc but not `pthread_create`.  Discussion in the
original merge request for the above commit also considered
`pthread_key_create`, `pthread_self`, and `pthread_attr_init`.  Every
symbol seems to have some reason it is not an appropriate choice.

Revert to the pre-3.14 behavior of using `pthread_create` pending
further investigation.

1 files changed, 3 insertions, 13 deletions

diff --git a/Modules/FindThreads.cmake b/Modules/FindThreads.cmake
index a2f3fa3017..919392ab9b 100644
--- a/Modules/FindThreads.cmake
+++ b/Modules/FindThreads.cmake
@@ -118,18 +118,8 @@ if(CMAKE_HAVE_PTHREAD_H)
   set(CMAKE_HAVE_THREADS_LIBRARY)
   if(NOT THREADS_HAVE_PTHREAD_ARG)
     # Check if pthread functions are in normal C library.
-    # If the pthread functions already exist in C library, we could just use
-    # them instead of linking to the additional pthread library. We could
-    # try to check any pthread symbol name, but here is an exception. If we
-    # use clang asan build, we will find the pthread_create() symbol in the
-    # libc(libasan). However, it doesn't have the full pthread implementation.
-    # So, we can't assume that we have the pthread implementation in libc
-    # using the pthread_create() checking here. Then, we turn to check the
-    # pthread_kill() symbol instead.  It is in the "signal.h" header, but
-    # the purpose of this check is to verify that the pthread API works with
-    # pure libc, so verify that "pthread.h" can be included too.
-    CHECK_SYMBOL_EXISTS(pthread_kill "signal.h;pthread.h" CMAKE_HAVE_LIBC_PTHREAD_KILL)
-    if(CMAKE_HAVE_LIBC_PTHREAD_KILL)
+    CHECK_SYMBOL_EXISTS(pthread_create pthread.h CMAKE_HAVE_LIBC_CREATE)
+    if(CMAKE_HAVE_LIBC_CREATE)
       set(CMAKE_THREAD_LIBS_INIT "")
       set(CMAKE_HAVE_THREADS_LIBRARY 1)
       set(Threads_FOUND TRUE)
@@ -154,7 +144,7 @@ if(CMAKE_HAVE_PTHREAD_H)
   _check_pthreads_flag()
 endif()
 
-if(CMAKE_THREAD_LIBS_INIT OR CMAKE_HAVE_LIBC_PTHREAD_KILL)
+if(CMAKE_THREAD_LIBS_INIT OR CMAKE_HAVE_LIBC_CREATE)
   set(CMAKE_USE_PTHREADS_INIT 1)
   set(Threads_FOUND TRUE)
 endif()