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 16aa7318846201eb0984facf869d3a31e61d02c9..2ce601e02cc4d8c7f2cdb87b1534c05ac629f289 100644
--- a/src/ppc/assembler-ppc.cc
+++ b/src/ppc/assembler-ppc.cc
@@ -257,6 +257,8 @@ 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;
 }