libgo: add type/const references to sysinfo.c

libgo: add type/const references to sysinfo.c

    This patch adds explicit references to various types and constants
    defined by the header files included by sysinfo.c (used to drive the
    generation of gen-sysinfo.go as part of the libgo build via the GCC
    "-fdump-go-spec" option).

    The intent is to enable clients to gather the same info generated by
    "-fdump-go-spec" by instead reading the generated DWARF from a
    sysinfo.o object file compiled with "-g". Some compilers (notably
    clang) try to omit DWARF records for a given type unless there is an
    explicit use of it in the translation unit; the additional references
    are to insure that everything we want to see in the DWARF shows up.

    Reviewed-on: https://go-review.googlesource.com/99063

From-SVN: r259868