runners: Intercept logs/printf and exclude from stack/heap measurements

Logging is one of those things that's very useful to keep around, but
has a high-risk of stack/heap costs that shouldn't count towards any
benchmarks (you can always disable logging).

So, lets exclude them from stack/heap measurements.

This could've been done by defining all of littlefs's LFS3_DEBUG/INFO/
WARN/ERROR macros, but intercepting printf directly is a bit less
tedious. As a plus, we eliminate logging costs from any other filesystem
we benchmark, without need to fiddle with everyone's logging APIs.

---

Hmm. Actually, now that I've done a test run, these changes seem to have
no effect.

Which makes sense in hindsight:

1. For efficiencies sake, printf likely tries to allocate infrequently.
   Maybe only during the first call?

   And we print the bench id before entering the bench.

2. The way our stack measurements work, we only count them if we enter a
   bd op or call BENCH_STACK_PAUSE().

   So any printfs encountered previously would have been ignored by our
   stack measurements.

Still, better safe than sorry.

runners/test_runner.h

@@ -44,16 +44,18 @@
 #endif
 
 // override LFS3_TRACE
+#ifndef LFS3_NO_TRACE
 void test_trace(const char *fmt, ...);
-
 #define LFS3_TRACE_(fmt, ...) \
-    test_trace("%s:%d:trace: " fmt "%s\n", \
-        __FILE__, \
-        __LINE__, \
-        __VA_ARGS__)
+    test_trace("%s:%d:trace: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
 #define LFS3_TRACE(...) LFS3_TRACE_(__VA_ARGS__, "")
 #define LFS3_EMUBD_TRACE(...) LFS3_TRACE_(__VA_ARGS__, "")
 #define LFS3_KIWIBD_TRACE(...) LFS3_TRACE_(__VA_ARGS__, "")
+#else
+#define LFS3_TRACE(...)
+#define LFS3_EMUBD_TRACE(...)
+#define LFS3_KIWIBD_TRACE(...)
+#endif
 
 
 // note these are indirectly included in any generated files