runtime: call execname and getpagesize on Solaris

    
    Interpreting auxv as []uintptr is incorrect on 64-bit big-endian,
    as auxv alternates a 32-bit int with a 64-bit pointer.
    
    Patch from Rainer Orth.
    
    Reviewed-on: https://go-review.googlesource.com/c/164739

From-SVN: r269315