Initial support for emitting unwinding information in perf jitdump.

src/x87/assembler-x87.cc

Index: src/x87/assembler-x87.cc
diff --git a/src/x87/assembler-x87.cc b/src/x87/assembler-x87.cc
index c7757a4d2a2b7c578e9a57c13e6da6f4c0a88218..708866132697a2f87253b62f378e47ab6fcd1531 100644
--- a/src/x87/assembler-x87.cc
+++ b/src/x87/assembler-x87.cc
@@ -259,6 +259,8 @@ void Assembler::GetCode(CodeDesc* desc) {
   desc->reloc_size = (buffer_ + buffer_size_) - reloc_info_writer.pos();
   desc->origin = this;
   desc->constant_pool_size = 0;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }