re PR go/77809 ("_LITTLE_ENDIAN" redefined)

	PR go/77809

    libgo: strip most C macros from runtime.inc
    
    The Go runtime package is picking up C macros from runtime_sysinfo.go
    and then re-exporting them to runtime.inc.  This can cause name
    conflicts.  Change the Makefile so that we only put the macros we need
    into runtime.inc.  These are the constants that are actually defined by
    Go code, not runtime_sysinfo.go.  There are only a few, so we can
    pattern match.
    
    This is an additional hack on runtime.inc.  The long term goal is to
    convert the runtime package to Go and eliminate runtime.inc entirely, so
    a few hacks seem acceptable.
    
    Fixes GCC PR 77809.

    Reviewed-on: https://go-review.googlesource.com/30167

From-SVN: r240724