src/profiler.c: Share more code between CPU and Memory profilers

src/profiler.c: Share more code between CPU and Memory profilers

* src/profiler.c (struct profiler_log): New type.
(make_log): Use it.
(cpu, memory): New vars to replace cpu_log, memory_log, cpu_gc_count,
and mem_gc_count.
(add_sample): New function, extracted from `handle_profiler_signal`.
(handle_profiler_signal, malloc_probe): Use it.
(Fprofiler_cpu_start, Fprofiler_memory_start): Adjust call to `make_log`.
(export_log): New function, extracted from `Fprofiler_cpu_log`.
(Fprofiler_cpu_log, Fprofiler_memory_log): Use it.
(syms_of_profiler, syms_of_profiler_for_pdumper): Adjust to new `cpu`
and `memory` vars.