bench: race busybox again, verify the wc oracle, average the speedup

Busybox wc is back in every suite, for shits and giggles. checkwc now
walks PATH and identifies each wc by its --version answer (coreutils and
fastwc respond; busybox names itself in the error it prints), so a wc
symlinked to fastwc is detected and skipped instead of silently racing
us against ourselves, and a missing coreutils is a clear configure
error. Every run now ends with the average speedup of fastwc against
coreutils and busybox, computed from the per-case ratios.

The fail-fast verdict now requires a measurable (>0ms) reference time,
so sub-millisecond cases stop flaking on startup noise, and the 100M
line monster is pinned back to the coreutils oracle instead of whatever
oracle was raced last.

benchmarks/test-all.sh

@@ -1,12 +1,22 @@
 #!/usr/bin/env bash
 # test-all.sh — compile the benchmark helper tools first, then run every
-# benchmark suite (words, lines incl. monsters, stdin). Exits non-zero if
-# any of them fails.
+# benchmark suite (words, lines incl. monsters, stdin) against every
+# oracle found (coreutils, plus busybox for shits and giggles). Exits
+# non-zero if any of them fails, and ends with the average speedup of
+# fastwc against each oracle.
 #
 # usage: ./test-all.sh
 set -u
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+# Share one ratios file across all suites so the final average covers
+# every case; each suite still races through its own process.
+RATIOS_FILE="$(mktemp /tmp/fastwc-ratios.XXXXXX)"
+export RATIOS_FILE
+
+source "$SCRIPT_DIR/std.sh"
 
 # 1. build the helper tools before running any benchmark so createtxt()
 #    can use the fast C generator instead of the slow shell fallback
@@ -29,6 +39,10 @@ rc_stdin=$?
 if [[ $rc_words -ne 0 || $rc_lines -ne 0 || $rc_stdin -ne 0 ]]; then
     printf '\ntest-all: FAILED (words=%s, lines=%s, stdin=%s)\n' \
         "$rc_words" "$rc_lines" "$rc_stdin" >&2
+    print_averages
+    rm -f "$RATIOS_FILE"
     exit 1
 fi
 printf '\ntest-all: all benchmarks passed\n'
+print_averages
+rm -f "$RATIOS_FILE"