Put cmd_run failure tracing behind an experimental flag

Author: rexim

nob.h

@@ -80,6 +80,8 @@
         but if you want to know what is discouraged you may want to enable this flag.
       - NOB_EXPERIMENTAL_DELETE_OLD - Experimental feature that automatically removes `nob.old` files. It's unclear how well
         it works on Windows, so it's experimental for now.
+      - NOB_EXPERIMENTAL_TRACE_CMD_RUN_FAIL - Log the locations of fail nob_cmd_run()-s. It's behind an experimental flag 
+        because I'm not sure how much it alters the UX of the library for other people, but this is something I personally need.
       - NOB_UNSTRIP_PREFIX - do not strip the `nob_` prefixes from non-redefinable names.
       - NOB_NO_ECHO - do not echo the actions various nob functions are doing (like nob_cmd_run(), nob_mkdir_if_not_exists(), etc).
 
@@ -1294,9 +1296,14 @@ NOBDEF int nob_nprocs(void)
 NOBDEF bool nob__cmd_run_opt_with_location(Nob_Cmd *cmd, const char *file, int line, Nob_Cmd_Opt opt)
 {
     bool ok = nob_cmd_run_opt(cmd, opt);
+#ifdef NOB_EXPERIMENTAL_TRACE_CMD_RUN_FAIL
     if (!ok) {
         nob_log(NOB_ERROR, "%s:%d: ERROR: cmd_run failed", file, line);
     }
+#else
+    NOB_UNUSED(file);
+    NOB_UNUSED(line);
+#endif // NOB_EXPERIMENTAL_TRACE_CMD_RUN_FAIL
     return ok;
 }