RFR(xs): 8229967: Enable thread local handshakes on zero

[Robbin Ehn]

Hi all, please consider.

Zero can have handshakes enabled.
This prepares the vm for removing global safepoints.

Built x64 and sanity tested. (should be platform independent)
x86 do not build for me due to workaround_expand_exec_shield_cs_limit.

Thanks, Robbin

diff -r 7c20dcb59a68 src/hotspot/cpu/zero/globalDefinitions_zero.hpp
--- a/src/hotspot/cpu/zero/globalDefinitions_zero.hpp	Mon Aug 19 13:43:51 2019 +0200
+++ b/src/hotspot/cpu/zero/globalDefinitions_zero.hpp	Wed Aug 21 10:02:44 2019 +0200
@@ -32,2 +32,4 @@

+#define THREAD_LOCAL_POLL
+
  #include <ffi.h>
diff -r 7c20dcb59a68 src/hotspot/cpu/zero/globals_zero.hpp
--- a/src/hotspot/cpu/zero/globals_zero.hpp	Mon Aug 19 13:43:51 2019 +0200
+++ b/src/hotspot/cpu/zero/globals_zero.hpp	Wed Aug 21 10:02:44 2019 +0200
@@ -78,3 +78,3 @@

-define_pd_global(bool, ThreadLocalHandshakes, false);
+define_pd_global(bool, ThreadLocalHandshakes, true);