refs #13945 CT sizeof(T) is wrong if T or any member is empty object + misc improvements in tsizeof

[timotheecour]

• refs CT sizeof(T) is wrong if T or any member is empty object #13945 (which was partially fixed by sizeof for empty objects/tuples should be 1; fixes #14690 #14751)

• add more tests

• add 2 failing tests commented out

• use a better implementation for c_sizeof: as mentioned in bugs with {.emit.} #13943, the previous implementation was not usable at block or function scope

• use a better implementation for c_alignof by directly using _Alignof

• move doAssert not failed to the end which is more robust

note:

#13945 is only partially fixed because there's 1 remaining item:

• dummy should only be inserted for C backend, not C++ backend, for reasons described in CT sizeof(T) is wrong if T or any member is empty object #13945

[Araq]

Don't request my review on drafts with red tests please. ;-)

[timotheecour]

Don't request my review on drafts with red tests please. ;-)

i turned it into a draft after seeing some of red tests; but i just found out i can un-request a review; in some rare cases I'll still ping you on drafts if I need help :)

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you think it is still a valid PR, please rebase it on the latest devel; otherwise it will be closed. Thank you for your contributions.