Add C++ API to get untrusted host time

[eddyashton]

Resolves #2523.

Adds the API get_untrusted_host_time_v1, which returns the host-written (UTC) time as a timespec.

Also adds an example endpoint using this in the nobuiltins app, and a few test calls to confirm the reported time is close enough to the true time.

[ghost]

add_untrusted_time_api@24693 aka 20210504.4 vs main ewma over 20 builds from 24352 to 24682

Click to see table

build_id	build_number	sb_sgx_cft^	sb_sgx_cft_mem	sb_sgx_bft^	sb_sgx_bft_mem	sb_ws_sgx_cft^	sb_ws_sgx_cft_mem	sb_sig_sgx_cft^	sb_sig_sgx_cft_mem	tpcc_sgx_cft^	tpcc_sgx_cft_mem	tpcc_sgx_bft^	tpcc_sgx_bft_mem	ls_sgx_cft^	ls_sgx_cft_mem	ls_ws_sgx_cft^	ls_ws_sgx_cft_mem	ls_jwt_sgx_cft^	ls_jwt_sgx_cft_mem	ls_js_sgx_cft^	ls_js_sgx_cft_mem	ls_js_jwt_sgx_cft^	ls_js_jwt_sgx_cft_mem	CHAMP put (/s)^	CHAMP get (/s)^
24352	20210428.8	28895.2	1.29803e+07	14498.9	3.84083e+07	33762.1	1.35046e+07	5044.93	1.00967e+07	6663.74	9.39828e+07	3393.1	1.66072e+08	24508.9	1.7961e+07	30331.2	1.95339e+07	4139.63	1.45532e+07	2079.75	8.2617e+06	1432.61	7.99955e+06	1.29587e+06	3.62478e+07
24374	20210428.14	29642.4	1.29803e+07	14141.4	3.73597e+07	32426.3	1.35046e+07	5193.36	1.0621e+07	6737.77	9.21478e+07	3400.48	1.64762e+08	22596.6	1.74367e+07	28415.2	1.74367e+07	4395.46	1.45532e+07	2029.57	8.52384e+06	1465.31	7.73741e+06	1.33332e+06	3.69675e+07
24388	20210428.19	27537.3	1.29803e+07	14386.1	3.70975e+07	34193.6	1.35046e+07	4513.3	1.03588e+07	6621.58	9.26721e+07	3453.72	1.6083e+08	23389.9	1.76989e+07	29303.9	1.95339e+07	4360.38	1.45532e+07	1997.49	8.52384e+06	1484.83	7.99955e+06	1.32848e+06	3.62471e+07
24417	20210428.28	27889.4	1.29803e+07	14659	4.57483e+07	31372.8	1.32424e+07	4942.76	1.00967e+07	6541.86	9.31964e+07	3376.01	1.55062e+08	22314.5	1.74367e+07	27595.7	1.76989e+07	3990.78	1.48153e+07	2022.42	1.11453e+07	1451.43	8.2617e+06	1.33654e+06	3.58663e+07
24438	20210428.32	28878.4	1.29803e+07	13946.9	3.70975e+07	33323.2	1.35046e+07	4897.49	1.03588e+07	6294.31	9.31964e+07	3398.9	1.62402e+08	21914.7	1.74367e+07	28948	1.76989e+07	4384.71	1.45532e+07	1961.69	1.16696e+07	1453.03	7.73741e+06	1.32436e+06	3.60563e+07
24487	20210429.4	27148	1.29803e+07	13733.5	3.81461e+07	33049.7	1.32424e+07	5374.23	1.0621e+07	6334.64	9.21478e+07	3067.47	2.68571e+08	23624.5	1.76989e+07	28208.1	1.76989e+07	4026.92	1.4291e+07	1951.07	8.2617e+06	1496.77	7.99955e+06	1.32453e+06	3.60563e+07
24492	20210429.5	27268.9	1.27181e+07	14052.4	3.76218e+07	29533.3	1.35046e+07	4932.77	1.00967e+07	6302.39	9.24099e+07	3239.5	2.15093e+08	24754.3	1.76989e+07	28947.3	1.76989e+07	4068.59	1.40289e+07	1938.36	8.2617e+06	1453.82	7.99955e+06	1.35745e+06	3.63114e+07
24502	20210429.9	26546.4	1.29803e+07	14672.1	3.84083e+07	33595.1	1.35046e+07	4975.21	1.03588e+07	6474.73	9.24099e+07	3431.58	1.54276e+08	23228.3	1.71746e+07	30183.1	1.7961e+07	4074.73	1.45532e+07	1998.9	1.08831e+07	1437.94	7.99955e+06	1.33142e+06	3.59298e+07
24511	20210429.11	29967.2	1.29803e+07	14185.6	3.91947e+07	34475.4	1.35046e+07	5416.95	1.03588e+07	6427.87	9.10992e+07	3464.18	1.51392e+08	22026.7	1.74367e+07	29712.9	1.7961e+07	4349.76	1.45532e+07	2081.75	8.52384e+06	1487.42	7.99955e+06	1.34576e+06	3.67684e+07
24526	20210429.15	29339.9	1.29803e+07	14726.7	3.7884e+07	33436.9	1.32424e+07	5439.19	1.0621e+07	6463.56	9.37206e+07	3300.53	1.9019e+08	23574.1	1.76989e+07	28025.5	1.76989e+07	4235.43	1.48153e+07	1978.29	8.52384e+06	1470.07	7.99955e+06	1.35314e+06	3.61837e+07
24544	20210429.18	26808.2	1.32424e+07	14938.1	4.10297e+07	33268.6	1.32424e+07	4866.27	1.00967e+07	6325.62	9.13613e+07	3408.75	1.52965e+08	24792.1	1.82232e+07	29967.8	1.76989e+07	4401.18	1.48153e+07	2011.91	8.2617e+06	1451.97	7.99955e+06	1.3708e+06	3.59292e+07
24551	20210429.21	25439	1.27181e+07	13367.6	3.7884e+07	28387.9	1.32424e+07	4977.33	1.03588e+07	6486.59	9.18856e+07	2891.19	2.05656e+08	23363	1.71746e+07	30101.9	1.76989e+07	3925.77	1.4291e+07	2075.49	8.52384e+06	1458.71	7.99955e+06	1.34215e+06	3.63121e+07
24567	20210429.25	26991	1.29803e+07	13575.8	3.86704e+07	33216.1	1.32424e+07	4860.98	1.0621e+07	6486.62	9.16235e+07	3411.9	1.77082e+08	24125.5	1.74367e+07	29101.7	1.7961e+07	4228.48	1.45532e+07	2077.86	8.2617e+06	1453.77	9.31027e+06	1.34497e+06	3.62478e+07
24584	20210430.1	28953.8	1.32424e+07	14670.6	3.7884e+07	30152	1.35046e+07	4796.8	1.0621e+07	6605.36	9.16235e+07	3323.05	1.47722e+08	23001.3	1.76989e+07	29445.5	1.76989e+07	4242.52	1.45532e+07	2058.09	8.52384e+06	1451.77	9.57242e+06	1.34844e+06	3.61199e+07
24587	20210430.2	28120.1	1.29803e+07	14524.9	3.94568e+07	34453.3	1.35046e+07	4920.3	1.00967e+07	6723.07	9.26721e+07	3030.36	1.9753e+08	22394.7	1.76989e+07	29226.1	1.7961e+07	3868.71	1.4291e+07	2007.56	1.00967e+07	1423.19	7.99955e+06	1.30611e+06	3.59292e+07
24604	20210430.7	26052.8	1.29803e+07	13873.6	3.81461e+07	34375.7	1.35046e+07	5276.97	1.21939e+07	6385.08	9.16235e+07	3353.43	1.78131e+08	24343.7	1.76989e+07	29897.1	1.76989e+07	3859.3	1.4291e+07	2052.38	8.52384e+06	1402.32	7.99955e+06	1.34294e+06	3.62471e+07
24616	20210430.10	28306.6	1.29803e+07	14294.7	3.76218e+07	31792.8	1.32424e+07	4471.42	1.00967e+07	6558.14	9.05749e+07	3426.68	1.50606e+08	22784.9	1.76989e+07	28840.2	1.76989e+07	4207.73	1.45532e+07	1965.97	8.52384e+06	1400.25	7.73741e+06	1.34276e+06	3.62478e+07
24640	20210430.18	24936.4	1.32424e+07	13727.2	3.76218e+07	32701.6	1.32424e+07	4841.66	1.00967e+07	6510.91	9.26721e+07	3346.24	1.68956e+08	23653.7	1.7961e+07	30023.9	1.76989e+07	4102.44	1.50774e+07	2039.69	8.52384e+06	1455.89	7.99955e+06	1.35538e+06	3.63121e+07
24665	20210430.25	28071.2	1.27181e+07	13753.2	3.73597e+07	31916.5	1.29803e+07	4528.1	1.03588e+07	6462.63	9.16235e+07	3412.93	1.67383e+08	22795.5	1.76989e+07	27710.3	1.74367e+07	4214.67	1.48153e+07	2107.05	1.11453e+07	1457.57	7.73741e+06	1.34303e+06	3.54933e+07
24682	20210504.1	29888.9	1.29803e+07	14073.7	4.10297e+07	33852.8	1.32424e+07	4887.24	1.00967e+07	6742.63	9.13613e+07	3472.05	1.73675e+08	23470.9	1.74367e+07	29675.4	1.76989e+07	4036.84	1.45532e+07	1993.47	8.2617e+06	1481.98	9.57242e+06	1.34879e+06	3.62478e+07