Bug 1312549 - use equality comparison rather than ordered comparison in ~GeckoChildProcessHost; r=billm

clang has recently made |x $RELATIONAL_OP 0|, where |x| is a variable of
pointer type, to be an error.  On Windows,
GeckoChildProcessHost::mChildProcessHandle is a HANDLE, which is really
just a pointer.  So the comparison |> 0| in ~GeckoChildProcessHost is
invalid.  Fortunately, we can use an equality comparison here and it
amounts to the same thing.

ipc/glue/GeckoChildProcessHost.cpp

@@ -120,7 +120,7 @@ GeckoChildProcessHost::~GeckoChildProcessHost()
 
   MOZ_COUNT_DTOR(GeckoChildProcessHost);
 
-  if (mChildProcessHandle > 0) {
+  if (mChildProcessHandle != 0) {
 #if defined(MOZ_WIDGET_COCOA)
     SharedMemoryBasic::CleanupForPid(mChildProcessHandle);
 #endif