Tell Valgrind about our ULT stacks so it doesn't get confused

This avoids reporting false-positive errors like the following:

==25331== Warning: client switching stacks?  SP change: 0xfff000508 --> 0x5a30a18
==25331==          to suppress, use: --max-stackframe=68608129776 or greater
==25331==
==25331== Invalid read of size 8
==25331==    at 0x569E4AC: swapcontext (swapcontext.S:93)
==25331==    by 0x56A07FF: ??? (in /lib/x86_64-linux-gnu/libc-2.19.so)
==25331==  Address 0x5a30bd0 is 256 bytes inside a block of size 1,064 alloc'd
==25331==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==25331==    by 0x5E80E4: CthCreateInner (libthreads-default.c:1714)
==25331==    by 0x5E828F: CthCreate (libthreads-default.c:1780)
==25331==    by 0x5E8E7C: ConverseInit (machine.c:331)
==25331==    by 0x51D9DD: main (main.C:18)

The Valgrind documentation explicitly recommends copying the header
included here into the client source tree, to avoid an external
dependency. The license is specifically geared to support this.

Change-Id: I26004af3edb7ac47931b80e78930c92857e31f67

src/conv-core/threads.c

@@ -106,6 +106,8 @@
 #include "conv-trace.h"
 #include <sys/types.h>
 
+#include "valgrind.h"
+
 #ifndef CMK_STACKSIZE_DEFAULT
 #define CMK_STACKSIZE_DEFAULT 32768
 #endif
@@ -167,6 +169,8 @@
   int        stacksize; /*Size of thread stack (bytes)*/
   struct CthThreadListener *listener; /* pointer to the first of the listeners */
 
+  unsigned int valgrindStackID;
+
 #if CMK_THREADS_BUILD_TLS
   tlsseg_t tlsseg;
 #endif
@@ -433,6 +437,9 @@ static void *CthAllocateStack(CthThreadBase *th,int *stackSize,int useMigratable
   }
   _MEMCHECK(ret);
   th->stack=ret;
+
+  th->valgrindStackID = VALGRIND_STACK_REGISTER(ret, ret + *stackSize);
+
   return ret;
 }
 static void CthThreadBaseFree(CthThreadBase *th)
@@ -468,6 +475,7 @@ static void CthThreadBaseFree(CthThreadBase *th)
   else if (th->stack!=NULL) {
     free(th->stack);
   }
+  VALGRIND_STACK_DEREGISTER(th->valgrindStackID);
   th->stack=NULL;
 }