Build prof_machdep.c if profiling.
Build prof_machdep.c if profiling.

Kernel profiling for amd64's (normal and high resolution) should now
compile and work as (un)well as on i386's.  It works better than user
profiling because:
- it uses _cyg_profile_func_*() instead of .mcount(), so it doesn't suffer
  from gcc misspelling .mcount as mcount.
- it doesn't neglect saving %rax in .mcount().

The SMP case hasn't been tested.  The high resolution subcase of this uses
the i8254, and as on i386's, the locking for this is deficient and the
i8254 is too inefficient.  The acpi timer is also too inefficient.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase