runtime: Remove confusion about split stack functions in backtrace.

R=iant
CC=gofrontend-dev
https://codereview.appspot.com/7237062
runtime: Recognize morestack.S if there is no function name.

R=iant
CC=gofrontend-dev
https://codereview.appspot.com/7232069
compiler: Don't emit multiple methods for identical unnamed structs.

R=iant
CC=gofrontend-dev
https://codereview.appspot.com/7262043
runtime: Correct test for morestack.S.

R=iant
CC=gofrontend-dev
https://codereview.appspot.com/7230061