LINK_SPEC. This solves a problem with the f77 frontend where
aproviding the -r8 option (use REAL*8) caused `cc' to ``forget'' to
pass the entry point to the linker.
Closes PR #gnu/644: f77 -r8
Reviewed by: watanabe@komadori.earth.s.kobe-u.ac.jp (Takeshi WATANABE)