[libmysql]Fix build error in linux.

[JackBoosY]

The reason for the build error in linux is that the macro CMAKE_SYSTEM_PROCESSOR is NOT set. So I modified the configure.cmake file.
Building libmysql in linux requires ncurses support(Which is not included in vcpkg), so I wrote a warning output in portfile.cmake. WARNING: It may cause CI build error.

And thanks @scttgs0 for his patch.

Related: #4616 #6389 #5046 #4409 #6365

[vicroms]

Also related: #5218

[vicroms]

/AzurePipelines run

[azure-pipelines]

No pipelines are associated with this pull request.

[vicroms]

Necessary dependencies where not installed in CI, they are now, so I'm triggering a new build.

The problem with this one, is that a ✔️ means that there are not regressions, NOT that the port is building successfully for x64-linux . So we have to be careful to merge it.

[JackBoosY]

/bin/bash failed with return code: 2
return code: 1


fi
[command]/bin/bash /Users/philc/vcpkg/myagent/_work/7/s/user_script.sh
/Users/philc/vcpkg/myagent/_work/7/s/user_script.sh: line 4: syntax error near unexpected token `fi'
/Users/philc/vcpkg/myagent/_work/7/s/user_script.sh: line 4: `fi'
##[section]Finishing: Setup Environment

Why?

[JackBoosY]

@Rastaban Can you look at it? PR-EAGER is blocked on the OSX step.