Initial support for emitting unwinding information in perf jitdump.

src/s390/assembler-s390.cc

Index: src/s390/assembler-s390.cc
diff --git a/src/s390/assembler-s390.cc b/src/s390/assembler-s390.cc
index cc9b8c7d047bb6a45c0aff00d6cc6e8d92f3e3f9..ee1b033c495a2ba2d5bca1c64d73f48e5f5da078 100644
--- a/src/s390/assembler-s390.cc
+++ b/src/s390/assembler-s390.cc
@@ -327,6 +327,8 @@ void Assembler::GetCode(CodeDesc* desc) {
   desc->instr_size = pc_offset();
   desc->reloc_size = (buffer_ + buffer_size_) - reloc_info_writer.pos();
   desc->origin = this;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }
 
 void Assembler::Align(int m) {