Putting C2 load barrier stub routines in separate blobs make the labels in print assembly show the type of the barrier. This simplifies debugging.

A load barrier slow path (that delegates to the stub routine) will have a stub name that reveals the barrier type, like this:

  0x00007f8fb91b4b58: lea 0x10(%r9),%r11
  0x00007f8fb91b4b5c: callq 0x00007f8fb9009a60 ; {runtime_call zgc_load_barrier_weak_stubs}
  0x00007f8fb91b4b61: jmpq 0x00007f8fb91b4a23