Mark CMake project explicitly as C++

[janisozaur]

This prevents checking of C compiler

[coveralls]

Coverage remained the same at 100.0% when pulling dcc83b7 on janisozaur:patch-1 into be35975 on skypjack:master.

[skypjack]

Good point, thanks. I'll merge it on master soon. 👍

[skypjack]

Unfortunately I must rollback this PR. If you enable BUILD_MOD, duktape is used to compile a test and therefore C is required. If you don't specify LANGUAGES, C and CXX are implicitly defined, that is all what is needed for EnTT and it's test suite.

[Innokentiy-Alaytsev]

What about marking test using duktape as C and CXX language project?

[skypjack]

@Innokentiy-Alaytsev Can we mark a single test? I didn't even know that.
It's fine for me. May I ask you to open another PR for that?

[Innokentiy-Alaytsev]

I'll check it out. The first thing I thought of was "We can set the language in test project declaration", but now I see that there are no separate projects for tests. I'll check out two ideas:

1. Create placeholder-ish project for all tests.

2. Set languages for separate target.

[Innokentiy-Alaytsev]

I'll prepare a pull request later this evening. My idea is to try to call enable_language if BUILD_MOD is true.

[skypjack]

Thank you. Really appreciated!! 😉

[skypjack]

Added to wip as you pointed out @Innokentiy-Alaytsev .
I put the call to enable_language in the file in the top directory as suggested by the documentation.