Most machines had undefined valu_t and redefined it to a different
type. Edit mach/*/as/mach0.c to remove such redefinitions, so the
next change to valu_t will affect all machines.
Edit mach/proto/as/comm0.h to change valu_t to int64_t, and add
uvalu_t and uint64_t.
Remove int64_t y_valu8 from the yacc %union, now that valu_t y_valu
can hold 64 bits. Replace y_valu8 with y_valu. The .data8 pseudo
becomes less special; it now accepts absolute expressions.
This change simplifies the assembler and seems to have no effect on
the assembled output. Among the files in share/ack/examples, the only
changes are in hilo_bas.* and startrek_c.linuxppc, but those files
seem to change whenever I rebuild them.
