add benchmark-interp tool

[cdetrio]

Example usage:

$ benchmark-interp add_main.wasm
parse succeeded...
execution succeeded.
run benchmark loop...
2019-07-29 16:22:39
Running benchmark-interp
Run on (12 X 2900 MHz CPU s)
CPU Caches:
  L1 Data 32K (x6)
  L1 Instruction 32K (x6)
  L2 Unified 262K (x6)
  L3 Unified 12582K (x1)
Load Average: 2.30, 1.88, 1.88
------------------------------------------------------
Benchmark            Time             CPU   Iterations
------------------------------------------------------
wabt_interp       97.3 us         97.1 us         6838

with a module add_main.wasm that succeeds:

(module
  (func $main (export "main")
    i32.const 5
    i32.const 5
    i32.add
    drop))

Given a module add_main_trap.wasm that fails:

(module
  (func $main (export "main")
    i32.const 5
    i32.const 5
    i32.add
    unreachable
    drop))

$ benchmark-interp add_main_trap.wasm
parse succeeded...
ERROR: execution failed.