ww: import toolchain — C bootstrap + ww-side self-host (phases 0-10)

C bootstrap (phases 0-9):
  cmd/wwc, cmd/6c, cmd/6a, cmd/6l, cmd/ww, rt, lib/*.

ww-side self-host (phase 10):
  selfhost/cmd/wwc — ww-cgen frontend; bootstrap fixed point.
  selfhost/cmd/6a  — assembler; byte-identical to C 6a (test 991).
  selfhost/cmd/6l  — linker w/ archive (.a) support; byte-identical
                     to C 6l (test 992).
  selfhost/cmd/ww  — driver (build/run/version); byte-identical to
                     C ww (test 993).

make test: 15/15. make bootstrap: ww2.s == ww3.s, ww2.o == ww3.o,
ww2 == ww3 byte-identical, with the full ww-tooled chain.

cmd/6a/lex.c

@@ -0,0 +1,31 @@
+/*
+ * lex.c — character-level helpers for 6a's line-oriented parser.
+ * The parser itself lives in parse.c; here we keep the tokenisers
+ * for identifiers and numbers so parse.c stays focused on syntax.
+ */
+#include "a.h"
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+a_isidstart(int c)
+{
+	return c == '_' || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+}
+
+int
+a_isidcont(int c)
+{
+	return a_isidstart(c) || (c >= '0' && c <= '9') || c == '.';
+}
+
+i64
+a_parsenum(const char *s, char **end)
+{
+	/* Let strtoll handle the sign itself: hand-stripping '-' then
+	 * negating the result fails for LLONG_MIN because the positive
+	 * magnitude (2^63) doesn't fit in long long, strtoll clamps to
+	 * LLONG_MAX, and the negation lands one short. */
+	return (i64)strtoll(s, end, 0);
+}