Merge pull request #2343 from philip-wernersbach/fix-pthreads-under-cpp

Fix issues with pthread_create when compiling under C++ mode.

lib/system/threads.nim

@@ -127,7 +127,7 @@ else:
     importc, header: "<pthread.h>".}
 
   proc pthread_create(a1: var TSysThread, a2: var TPthread_attr,
-            a3: proc (x: pointer) {.noconv.}, 
+            a3: proc (x: pointer): pointer {.noconv.}, 
             a4: pointer): cint {.importc: "pthread_create", 
             header: "<pthread.h>".}
   proc pthread_join(a1: TSysThread, a2: ptr pointer): cint {.
@@ -315,7 +315,7 @@ when defined(windows):
     threadProcWrapperBody(closure)
     # implicitly return 0
 else:
-  proc threadProcWrapper[TArg](closure: pointer) {.noconv.} = 
+  proc threadProcWrapper[TArg](closure: pointer): pointer {.noconv.} = 
     threadProcWrapperBody(closure)
 {.pop.}
 

tests/cpp/tthread_createthread.nim

@@ -0,0 +1,14 @@
+discard """
+  cmd: "nim cpp --hints:on --threads:on $options $file"
+"""
+
+proc threadMain(a: int) {.thread.} =
+    discard
+
+proc main() =
+    var thread: TThread[int]
+
+    thread.createThread(threadMain, 0)
+    thread.joinThreads()
+
+main()