Dump instruction set features in .cfg

This commit adds a compilation block at the beginning of the .cfg
dumped by the optimizing compiler when --dump-cfg is enabled.

The compilation block appears in the following form:

begin_compilation
  name "isa_features:feature1,-feature2"
  method "isa_features:feature1,-feature2"
  date 1580721972
end_compilation

This compilation block dump is passed to checker script (see
https://android-review.googlesource.com/c/platform/art/+/1290997)
for checking if a certain instruction set feature was used at compile
time.

Author:    Fabio Rinaldi
Committer: Artem Serov

Bug: 147876827
Test: ./art/tools/checker/run_unit_tests.py
Test: test.py --target --optimizing
Change-Id: If4309af4bab892f715aad1d3bd338f8ee11e497c
3 files changed