build: make systemtap probes work with gyp build

The following now works though the used approach is nothing to write
home about:

  $ ./gyp_uv -Duv_use_dtrace=true
  # <output elided>
  $ make -C out BUILDTYPE=Debug
  # <output elided>
  $ cd out/Debug && stap -L 'process("./run-tests").mark("*")'
  process("./run-tests").mark("tick__start") $arg1:long $arg2:long
  process("./run-tests").mark("tick__stop") $arg1:long $arg2:long