Add O2 and LTCG flag for MSVC Windows branch

[VOM7HC]

CMakeList current just optimize for Unix. Clang and GNU GCC have O3 flag for optimize performance code. MSVC doesn't have O3, so I use O2 flag for speed and LTCG for force compiler use inline function every time.
In my personal test, I saw in task manager, use O2 and LTCG help to improve estimate 2% ~ 5% CPU usage.

LTCG flag
O2 flag

[vi3itor]

Hi @WesleyKhoiVo! Thanks for your contribution! I will check it out after I finish with the PR for gfootball.
I plan to finalize the changes and merge windows branch once I have enough time.

I thought that cmake's --config Release adds O2 flag automatically, but indeed LTCG might squeeze in some additional performance.

[VOM7HC]

I can't find any document or link say cmake add O2 automatically when we switch to Release, so I added it manually.

Note: it just improve CPU usage, FPS still drop sometime, so we need more time to cleanup game engine

[vi3itor]

I'm testing the PR and get the following warning after building:
LINK : /LTCG specified but no code generation required; remove /LTCG from the link command line to improve linker performance.
Do you have it too?

[VOM7HC]

Update comment:
MSVC require so much. I use Visual Studio solution, which generated by CMake, then I added LTCG flag in properties window to build, for test performance. It may be auto add or remove some other flags when I add LTCG. Then I added LTCG back to cmakelist.txt. Now I will find solution, then update it again
Reference issue and fix it from MS forum:
Compiling with "Whole Program Optimization" but linker says no code generation required

[VOM7HC]

And linker performance is just effect to compile time, not effect to runtime anyway 😄

[VOM7HC]

Hi @vi3itor, can you recheck again?

[vi3itor]

I checked, the warning is gone.
Funny, the total size of the *.lib files is 1.3 Gb, with blunted2.lib along being 706 Mb. Since only an executable and .dll are required for running the game I will add an installation script to compile the game and remove unnecessary files. Probably even better is to improve CMakeLists.txt.

[VOM7HC]

Yeah, I think I will remove *.lib in another PR. This PR is just improve performance via flags compiler.