Initial support for emitting unwinding information in perf jitdump.

src/ppc/assembler-ppc.cc

Index: src/ppc/assembler-ppc.cc
diff --git a/src/ppc/assembler-ppc.cc b/src/ppc/assembler-ppc.cc
index f384a5fe645a0cd7b1c7859e7782238b66b614ee..3aa3b3b3622a252cac9906acea219fec8ec655ed 100644
--- a/src/ppc/assembler-ppc.cc
+++ b/src/ppc/assembler-ppc.cc
@@ -284,6 +284,8 @@ void Assembler::GetCode(CodeDesc* desc) {
   desc->constant_pool_size =
       (constant_pool_offset ? desc->instr_size - constant_pool_offset : 0);
   desc->origin = this;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }