[Trivial] add func attribs to class Declaration final helpers

[ghost]

The same was asked in #7569 so there no reason not to add the attribs to the other helpers.

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[PetarKirov]

LGTM

[JinShil]

Does the const on these affect the C++ interface?

[ghost]

@ibuclaw, about the c++ interface ?

[PetarKirov]

@bbasile sorry, I merged your changes prematurely. You also need to update https://github.com/dlang/dmd/blob/master/src/dmd/declaration.h by adding const to all of the methods that you modified on the D side.

[PetarKirov]

I missed that, because I thought the auto-tester will check the C++ headers, courtesy of #7520. @ibuclaw how is that we're successfully linking (as seen in https://auto-tester.puremagic.com/show-run.ghtml?projectid=1&runid=2980879&dataid=21094560&isPull=true):

c++ -c -o../generated/linux/release/64/cxxfrontend.o -Wno-deprecated -Wstrict-aliasing -Werror -fno-exceptions -fno-rtti -D__pascal= -DMARS=1 -DTARGET_LINUX=1 -DDM_TARGET_CPU_X86=1 -m64 -fPIC -std=gnu++98 -O2 -Idmd -Idmd/root -Wuninitialized -MMD -MF ../generated/linux/release/64/cxxfrontend.deps tests/cxxfrontend.c

)
while having a CV-qualifier mismatch?

[PetarKirov]

Actually, since the functions are final (i.e. non-virtual) they are not part of the vtable, hence why we have implementations of those functions both in C++ and D. @bbasile you don't need to update anything on the C++ side, sorry for the confusion.

[ghost]

NP. The other PR is here in case of.

[ibuclaw]

You need to use the function in c++ in order to see the mismatch.