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/wwc/err.c

@@ -0,0 +1,76 @@
+/*
+ * err.c — diagnostics.
+ *
+ * fatal	prints, sets exit(1).
+ * errorf	prints with source location, increments nerrors.
+ * warnf	prints with source location, increments nwarnings.
+ *
+ * Plan 9 style: short, no levels beyond fatal/error/warn, no colour.
+ */
+#include "ww.h"
+#include <stdlib.h>
+#include <string.h>
+
+Pos	noPos = { "<none>", 0, 0 };
+int	nerrors;
+int	nwarnings;
+FILE	*errout;	/* set by main; defaults to stderr */
+
+static FILE *
+out(void)
+{
+	return errout ? errout : stderr;
+}
+
+static void
+prefix(Pos p)
+{
+	FILE *f = out();
+	if (p.file == NULL)
+		p = noPos;
+	if (p.line > 0)
+		fprintf(f, "%s:%d:%d: ", p.file, p.line, p.col);
+	else
+		fprintf(f, "%s: ", p.file);
+}
+
+void
+fatal(const char *fmt, ...)
+{
+	FILE *f = out();
+	va_list ap;
+	fprintf(f, "ww: ");
+	va_start(ap, fmt);
+	vfprintf(f, fmt, ap);
+	va_end(ap);
+	fprintf(f, "\n");
+	exit(1);
+}
+
+void
+errorf(Pos p, const char *fmt, ...)
+{
+	FILE *f = out();
+	va_list ap;
+	prefix(p);
+	fprintf(f, "error: ");
+	va_start(ap, fmt);
+	vfprintf(f, fmt, ap);
+	va_end(ap);
+	fprintf(f, "\n");
+	nerrors++;
+}
+
+void
+warnf(Pos p, const char *fmt, ...)
+{
+	FILE *f = out();
+	va_list ap;
+	prefix(p);
+	fprintf(f, "warning: ");
+	va_start(ap, fmt);
+	vfprintf(f, fmt, ap);
+	va_end(ap);
+	fprintf(f, "\n");
+	nwarnings++;
+}