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 1d206903b044ced12e26806904d108b29f672f87..07ef6c0742102530b3d0f9ecb8246e9e2282765d 100644
--- a/src/s390/assembler-s390.cc
+++ b/src/s390/assembler-s390.cc
@@ -300,6 +300,8 @@ 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) {