Prefer -pthread flag on UNIX (#28272)

CMakeLists.txt

@@ -293,6 +293,16 @@ if (gRPC_XDS_USER_AGENT_IS_CSHARP)
   add_definitions("-DGRPC_XDS_USER_AGENT_NAME_SUFFIX=\"csharp\"" "-DGRPC_XDS_USER_AGENT_VERSION_SUFFIX=\"2.44.0-dev\"")
 endif()
 
+if(UNIX)
+  # -pthread does more than -lpthread
+  set(THREADS_PREFER_PTHREAD_FLAG ON)
+  find_package(Threads)
+  set(_gRPC_ALLTARGETS_LIBRARIES ${CMAKE_DL_LIBS} m Threads::Threads)
+  if(_gRPC_PLATFORM_LINUX OR _gRPC_PLATFORM_POSIX)
+    set(_gRPC_ALLTARGETS_LIBRARIES ${_gRPC_ALLTARGETS_LIBRARIES} rt)
+  endif()
+endif()
+
 include(cmake/abseil-cpp.cmake)
 include(cmake/address_sorting.cmake)
 include(cmake/benchmark.cmake)
@@ -304,14 +314,6 @@ include(cmake/upb.cmake)
 include(cmake/xxhash.cmake)
 include(cmake/zlib.cmake)
 
-if(_gRPC_PLATFORM_MAC OR _gRPC_PLATFORM_IOS)
-  set(_gRPC_ALLTARGETS_LIBRARIES ${CMAKE_DL_LIBS} m pthread)
-elseif(_gRPC_PLATFORM_ANDROID)
-  set(_gRPC_ALLTARGETS_LIBRARIES ${CMAKE_DL_LIBS} m)
-elseif(UNIX)
-  set(_gRPC_ALLTARGETS_LIBRARIES ${CMAKE_DL_LIBS} rt m pthread)
-endif()
-
 if(WIN32)
   set(_gRPC_BASELIB_LIBRARIES ws2_32 crypt32)
 endif()

templates/CMakeLists.txt.template

@@ -331,6 +331,16 @@
     add_definitions("-DGRPC_XDS_USER_AGENT_NAME_SUFFIX=\"csharp\"" "-DGRPC_XDS_USER_AGENT_VERSION_SUFFIX=\"${settings.csharp_version}\"")
   endif()
 
+  if(UNIX)
+    # -pthread does more than -lpthread
+    set(THREADS_PREFER_PTHREAD_FLAG ON)
+    find_package(Threads)
+    set(_gRPC_ALLTARGETS_LIBRARIES <%text>${CMAKE_DL_LIBS}</%text> m Threads::Threads)
+    if(_gRPC_PLATFORM_LINUX OR _gRPC_PLATFORM_POSIX)
+      set(_gRPC_ALLTARGETS_LIBRARIES <%text>${_gRPC_ALLTARGETS_LIBRARIES}</%text> rt)
+    endif()
+  endif()
+
   include(cmake/abseil-cpp.cmake)
   include(cmake/address_sorting.cmake)
   include(cmake/benchmark.cmake)
@@ -342,14 +352,6 @@
   include(cmake/xxhash.cmake)
   include(cmake/zlib.cmake)
 
-  if(_gRPC_PLATFORM_MAC OR _gRPC_PLATFORM_IOS)
-    set(_gRPC_ALLTARGETS_LIBRARIES <%text>${CMAKE_DL_LIBS}</%text> m pthread)
-  elseif(_gRPC_PLATFORM_ANDROID)
-    set(_gRPC_ALLTARGETS_LIBRARIES <%text>${CMAKE_DL_LIBS}</%text> m)
-  elseif(UNIX)
-    set(_gRPC_ALLTARGETS_LIBRARIES <%text>${CMAKE_DL_LIBS}</%text> rt m pthread)
-  endif()
-
   if(WIN32)
     set(_gRPC_BASELIB_LIBRARIES ws2_32 crypt32)
   endif()