w6c+w6a+selfhost+lib: cgen+asm bugs surfaced by hash modules

Seven fixes across the toolchain, plus three new lib/hash modules
(adler32, crc16, crc32) that surfaced them.

  1. `~x` on u8/u16/u32 left the upper bits set: NOTQ inverts the
     whole 64-bit register and nothing trimmed it back to type
     width, so a returned `u16` would compare 64-bit against a
     typed literal and disagree. Both stages now mask after NOTQ
     for narrow unsigned: AND $0xFF/0xFFFF for u8/u16, MOVL r,r for
     u32 (ANDQ $0xFFFFFFFF sign-extends imm32 and is a no-op).
     Signed narrows stay sign-extended and need no fix-up. See
     cmd/w6c/cgen.c N_UN TK_TILDE and selfhost cgenexpr.ww cgun
     TK_TILDE with new nodeprimwidth helper.

  2. w6a had no D_CONST immediate path for ANDQ / ORQ. cgen would
     emit `ANDQ $65535, AX` and the rr encoder silently wrote
     `21 /r` with garbage reg fields — the mask never happened.
     Added `81 /4` (AND) and `81 /1` (OR) imm32 paths in both
     cstage and selfhost w6a. The ~width fix above depends on this.

  3. `s: []u8` cast as a direct fn argument produced a 0-length
     slice. cgexpr for N_CAST left (AX=ptr, BX=len) from the str
     source but never set CX (cap), and the arg-push fallback only
     pushed AX. cgcast now synthesises CX=BX when target is slice
     and source is str; node_isslice / arg-push recognise
     cast-to-slice and emit the full (cap, len, ptr) triple. Both
     stages.

  4. `*[N]T` element-store used 8-byte stride + MOVQ regardless of
     T's width. Indexing `buf: *[4]u16` would step 8 bytes and
     write 8 bytes per element. Added idx_eff (drills *[N]T → T)
     in cstage and the matching pointer-array drill in selfhost
     elemsizeof. Also added MOVW / MOVZWQ / MOVSWQ to w6c, w6a,
     and selfhost mirrors so 2-byte element stores/loads use the
     right opcode (was falling through to MOVQ and trailing 6 bytes
     into the next slot).

  5. Slicing a top-level fixed array (`g[0:n]` where `g: [N]T` is
     a global) computed the base from BP instead of the symbol —
     localfind returned 0 and the cgen treated it as a local at
     offset 0. Both N_SLICE-as-expression (cgslice) and N_SLICE-
     as-call-arg paths now check let_islet / letvartnode and emit
     LEAQ name(SB) when the base is a global array (or MOVQ
     name(SB) for a global slice/pointer base). Both stages.

  6. Top-level `let arr: [N]T = [v0, v1, ...]` link-failed on
     cstage — emit_lets bailed when it saw N_ARRLIT init on an
     array type, and the sz==8 scalar path then misemitted any
     8-byte-sized array (e.g. [4]u16, [8]u8) as a single quad.
     emit_lets now walks N_ARRLIT, evaluates each element as an
     int/rune/bool/nil literal, packs per-element bytes
     little-endian, and honours the trailing `...` repeat marker.
     Selfhost already handled the literal-init path; fixed the
     parallel sz==8 duplicate-DATAW emit on its side (the array
     and the scalar paths both fired, last write winning at link
     but the duplicate broke cross-stage byte-identicality on user
     code with this shape).

  7. w6a's per-line input buffer was a 1KB stack `char buf[1024]`.
     A `DATAW` for a [256]u16 emits ~2080 bytes on one line, which
     truncated mid-escape; the assembler then re-parsed the
     remaining tail as garbage opcodes ("unknown opcode"). Bumped
     cstage w6a to a 32K static buffer (selfhost w6a already
     allocated per-line via amalloc).

  lib: lib/hash/adler32, lib/hash/crc16, lib/hash/crc32 — pure
  buffer-subset shape (matching lib/hash/fnv), with per-module
  *_test.ww runnable via `ww test lib/hash/<name>`. Adler-32 plus
  CRC-16 (CCITT/CMDA2000/DECT/ANSI) and CRC-32 (IEEE/Castagnoli/
  Koopman) cover Hare's reference vectors bit-for-bit. Wired into
  test/wcc/900_stdlib.c. .gitignore: lib/**/*.s,*.o so `ww test`
  droppings stay untracked.

`make test` (26/26), `make bootstrap` (ww2≡ww3≡ww4), and per-module
`ww test` all pass. cgen output is byte-identical across cstage and
selfhost for every repro that previously diverged.

cmd/w6a/parse.c

@@ -83,8 +83,9 @@ opcode_lookup(const char *m)
 {
 	struct { const char *m; int op; } tab[] = {
 		{ "MOVQ", A_MOVQ }, { "MOVL", A_MOVL },
-		{ "MOVB", A_MOVB }, { "MOVZBQ", A_MOVZBQ },
-		{ "MOVSXD", A_MOVSXD },
+		{ "MOVW", A_MOVW }, { "MOVB", A_MOVB },
+		{ "MOVZBQ", A_MOVZBQ }, { "MOVZWQ", A_MOVZWQ },
+		{ "MOVSXD", A_MOVSXD }, { "MOVSWQ", A_MOVSWQ },
 		{ "MOVSD", A_MOVSD },
 		{ "ADDSD", A_ADDSD },{ "SUBSD", A_SUBSD },
 		{ "MULSD", A_MULSD },{ "DIVSD", A_DIVSD },
@@ -263,7 +264,10 @@ parse_operand(Asm *a, const char *s, Aoperand *out)
 int
 a_parse(Asm *a)
 {
-	char buf[1024];
+	/* Big enough for a DATAW emitting a [256]u32 table (1024 bytes
+	 * → ~4100 chars of `\xNN` escapes plus directive boilerplate).
+	 * Selfhost w6a allocates per-line; this is the cstage equivalent. */
+	static char buf[32768];
 	char *line;
 	size_t len;
 	const char *pending_label = NULL;