Add PGO builds

[chfast]

The PGO builds give good boost to the performance, but we need to select out training set.

Comparing o/master to ../pgouse/o/master
Benchmark                                                     Time             CPU      Time Old      Time New       CPU Old       CPU New
------------------------------------------------------------------------------------------------------------------------------------------
fizzy/execute/blake2b/512_bytes_rounds_1                   -0.1681         -0.1740            99            82            99            82
fizzy/execute/blake2b/512_bytes_rounds_16                  -0.2512         -0.2512          1503          1125          1503          1125
fizzy/execute/ecpairing/onepoint                           -0.1878         -0.1878        473759        384788        473721        384762
fizzy/execute/keccak256/512_bytes_rounds_1                 -0.3023         -0.3023           116            81           116            81
fizzy/execute/keccak256/512_bytes_rounds_16                -0.3153         -0.3152          1713          1173          1713          1173
fizzy/execute/memset/256_bytes                             -0.2147         -0.2147             8             6             8             6
fizzy/execute/memset/60000_bytes                           -0.2239         -0.2239          1659          1287          1659          1287
fizzy/execute/mul256_opt0/input1                           -0.3080         -0.3079            33            23            33            23
fizzy/execute/ramanujan_pi/33_runs                         -0.3250         -0.3250           151           102           151           102
fizzy/execute/sha1/512_bytes_rounds_1                      -0.2244         -0.2244           104            81           104            81
fizzy/execute/sha1/512_bytes_rounds_16                     -0.2124         -0.2124          1443          1137          1443          1137
fizzy/execute/sha256/512_bytes_rounds_1                    -0.2048         -0.2048            97            77            97            77
fizzy/execute/sha256/512_bytes_rounds_16                   -0.1844         -0.1844          1323          1079          1323          1079
fizzy/execute/taylor_pi/pi_1000000_runs                    -0.0811         -0.0812         42727         39260         42724         39257
fizzy/execute/micro/eli_interpreter/exec105                -0.2854         -0.2854             6             4             6             4
fizzy/execute/micro/factorial/20                           -0.1208         -0.1208             1             1             1             1
fizzy/execute/micro/fibonacci/24                           -0.1348         -0.1348          5828          5042          5827          5042
fizzy/execute/micro/host_adler32/1                         -0.1522         -0.1522             0             0             0             0
fizzy/execute/micro/host_adler32/1000                      -0.2068         -0.2066            33            26            33            26
fizzy/execute/micro/icall_hash/1000_steps                  -0.1021         -0.1021            72            65            72            65
fizzy/execute/micro/spinner/1                              -0.1430         -0.1430             0             0             0             0
fizzy/execute/micro/spinner/1000                           -0.2250         -0.2250            10             8            10             8

[axic]

Looks nice! What set did you run PGO on?

[chfast]

Just fizzy-bench.