Warnings generated when building workerd

[anonrig]

Ref: https://github.com/cloudflare/workerd/actions/runs/15830678878/job/44622337703?pr=4394

INFO: From Compiling core/src/walltime.cpp:
external/codspeed/core/src/walltime.cpp:21:14: warning: unused variable 'IQR_OUTLIER_FACTOR' [-Wunused-const-variable]
   21 | const double IQR_OUTLIER_FACTOR = 1.5;
      |              ^~~~~~~~~~~~~~~~~~
external/codspeed/core/src/walltime.cpp:22:14: warning: unused variable 'STDEV_OUTLIER_FACTOR' [-Wunused-const-variable]
   22 | const double STDEV_OUTLIER_FACTOR = 3.0;
      |              ^~~~~~~~~~~~~~~~~~~~
2 warnings generated.