MIPS: Avoid using dd() in Prologue when --optimize-for-size.

Port: r17485 (0d82025)

Original commit message:
When --optimize-for-size is true, the prologue generation outputs the
pre-aging code stub address directly to the instruction stream. Previously
this was done using dd() which failed if there was any pending constant
pool entries left to be written. This CL introduces an emit_code_stub_address()
for this purpose instead.

BUG=v8:2968

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17508 ce2b1a6d-e550-0410-aec6-3dcde31c8c00