[Fix CMake for Clang users on Windows]

[Milerius]

Well, MSVC is not the only compiler on Windows, we use also Clang that use the same compiler flags as MSVC (clang-cl)

According to that, when you detect clang we also should detect platform.

[coveralls]

Coverage remained the same at 100.0% when pulling 1ed0a9f on Milerius:patch-1 into be35975 on skypjack:master.

[Innokentiy-Alaytsev]

Hello!

I'm not sure that $<PLATFORM_ID:MSVC> check will work. I used this pull-request as an example of using generator expressions and $<PLATFORM_ID:MSVC> did not work at all, because under MSVC PLATFORM_ID equals Windows.

[skypjack]

@Innokentiy-Alaytsev he updated it. Does it work as expected now?

[Milerius]

Hello!

I'm not sure that $<PLATFORM_ID:MSVC> check will work. I used this pull-request as an example of using generator expressions and $<PLATFORM_ID:MSVC> did not work at all, because under MSVC PLATFORM_ID equals Windows.

Just a typo.

[Innokentiy-Alaytsev]

Yes, it works fine. Sorry, if I looked into a wrong commit.

[skypjack]

Don't worry. Thank you for trying it. 👍

[skypjack]

We can merge this line and the one below as:

INTERFACE $<$<AND:$<CONFIG:Release>,$<CXX_COMPILER_ID:Clang>,$<OR:$<PLATFORM_ID:Darwin>,$<PLATFORM_ID:Linux>>>:-O2>

May I ask you to integrate the PR? Otherwise I can merge it on a separate branch and edit the file before to merge it on master.

[Milerius]

If you can edit it on your side is great I used the GitHub web editor !

I'm applying the changes on my side directly.

[Milerius]

maybe we can add a tests ta compile with clang on appveyor ?

cmake ../ -G "%GENERATOR%" -A %platform% -DCMAKE_BUILD_TYPE=%BUILD_TYPE% -T "ClangCl" -DCMAKE_CXX_COMPILER="C:/Program Files/LLVM/bin/clang-cl.exe"

platform: x64
GENERATOR: Visual Studio 16 2019
BUILD_TYPE: Debug

[skypjack]

clang is tested already on two platforms. I don't think this will add much to the build system tbh.