PR go/79037
    compiler, runtime: align gc data for m68k
    
    The current GC requires that the gc data be aligned to at least a 4
    byte boundary, because it uses the lower two bits of the address for
    flags (see LOOP and PRECISE in runtime/mgc0.c).  As the gc data is
    stored as a [...]uintptr, that is normally always true.  However, on
    m68k, that only guarantees 2 byte alignment.  Fix it by forcing the
    alignment.
    
    The parfor code used by the current GC requires that the parfor data
    be aligned to at least an 8 byte boundary.  The code in parfor.c
    verifies this.  This is normally true, as the data uses uint64_t
    values, but, again, this must be enforced explicitly on m68k.
    
    Fixes GCC PR 79037.
    
    Reviewed-on: https://go-review.googlesource.com/35478

From-SVN: r244824