Detailed Time break-down compilation mode

[rbertran]

Enable a timing mode when compiling that collects the time spent in each phase.

Regarding the breakdown, I was thinking in the following categories:

• Application time
• Profiler time
  • Init time (fork + first instrumentation)
  • start region of interest time (fix traps and insert calls)
  • end region of interest time (fix traps and insert calls)
• Support library time:
  • protect time
    • protect mem, system call time
    • IO time (write regs to disk)
    • other protect time (e.g.read all registers state, etc.)
  • unprotect time
    • unprotect system call time
    • other protect time
  • sighandler time
    • IO time (write)
    • unprotect system call time
    • other sighandler time

Regarding on how to implement it:

This should a be a configuration option during the compilation (e.g. -DTIMING in cmake), so that we can remove the timing overhead when needed. We need to implement this using architecture specific low level mechanisms when possible (e.g. STCKE instructions in Z, or MFTB in POWER) to read the time. Much faster: 1 instruction vs. 1 system call . If TIMING is enabled, reports are generated in stdout by default or in a file if TIMING_REPORT_FILE environment variable is defined with a filename.

[rbertran]

Compute totals time for each category above, and also:
Average and std. deviation (using Welford's online algorithm https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance)