libgo: If compiler can split-stack and linker can not, use -fno-split-stack.

libgo: If compiler can split-stack and linker can not, use -fno-split-stack.

    If the compiler supports split-stack but we are using a gold linker that
    does not, as happens on PPC with current GCC but old gold, then we need
    to compile the Go code with -fno-split-stack to avoid a linker error
    avoid the inability to call from split-stack code to non-split-stack
    code.

    Reviewed-on: https://go-review.googlesource.com/14598

From-SVN: r227811