A64: clean up pending reloc info if code generation was aborted.

This fixes assertion failure in destructor of Assembler.

BUG=352659
LOG=N
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/206213002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20100 ce2b1a6d-e550-0410-aec6-3dcde31c8c00