selfhost/cmd/6c/main.ww is a thin packaging of the wwc cgen — slurp
a .ww file, run lex+parse+cgen, write Plan 9 amd64 asm to the path
given by -o. The cgen routines in selfhost/cmd/wwc/cgen.ww write
directly to fd 1, so we use dup2 to redirect stdout into the
output file rather than thread an fd through every emit helper.
Adds the SYS_DUP2=33 wrapper in lib/os.
Makefile wires $(BIN)/6c_ww alongside the other wwstage tools and
adds $(BIN)/test_6c_ww to the TESTS list.
test/wwc/994_6c_ww.c diffs 6c_ww byte-for-byte against
`wwdump_ww -c` on five in-source programs plus the four selfhost
main.combined.ww files: same cgen reached through two binaries, so
any divergence is a packaging bug in selfhost/cmd/6c.
We deliberately don't diff against C-side 6c here — 990 probe 5
already covers that on the subset the ww cgen handles today.
Hojun-Cho
218d8469ff