When running with -asm-verbose, assembler directives like the following are generated:

  lv$__123 = 16

These symbols show up in "nm" output of the .o file, and cause inconsistencies in symbol numbering between filetype=asm and filetype=obj, when doing szbuild.py bisection debugging.

The fix is to prepend ".L" to the symbol name, so that the assembler treats it as local.  E.g.:

  .L$lv$__123 = 16

BUG= none
R=eholk@chromium.org

Review URL: https://codereview.chromium.org/2095633002 .