photon 0.8 & refactor build

[WaberZhuang]

What this PR does / why we need it:

• bump photon to release/0.8
• fix compiler warnings & build with -Wall -Werror
• refactor cmake build

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[liulanzheng]

Why not use photon 0.9? And cache source code can delete the cache that should be used in photon. Multi vcpu can be used for acceleration because file cache supports vcpu now.

[liulanzheng]

@WaberZhuang liulanzheng@125ac95
You can refer to my commit to help you compile successfully by using photon v0.9.6, but I've forgotten how multi-vCPU was implemented before, and I'm not sure about the performance of my commit either