RFR 8237753: 32-bit builds are broken after JDK-8230594

[Patricio Chilano]

Hi,

This small fix is to address the build failures on arm32 after my change 
"8230594: Allow direct handshakes without VMThread intervention". Member 
_pending_threads should be 32 bits:

diff --git a/src/hotspot/share/runtime/handshake.cpp 
b/src/hotspot/share/runtime/handshake.cpp
--- a/src/hotspot/share/runtime/handshake.cpp
+++ b/src/hotspot/share/runtime/handshake.cpp
@@ -40,7 +40,7 @@

  class HandshakeOperation: public StackObj {
    HandshakeClosure* _handshake_cl;
-  int64_t _pending_threads;
+  int32_t _pending_threads;
    bool _executed;

Bug: https://bugs.openjdk.java.net/browse/JDK-8237753

Thanks!

Patricio