[Lazarus] Trunk compilation broken by changing StrikeThrough property name

[Alexander Klenin]

Revision 39879 introduced some compile-time conditionals
apparently intended to fix a typo while breaking user code,
but not Lazarus code.

Unfortunately, Lazarus stopped compiling for me since that revision.
I have committed a quick fix in r39885, but I do not understand
why that change was made in such a strange manner and
how did it compile for the committer -- I tested and both 2.6 and 2.7
give same error.

So please review -- I am afraid I am missing something.

--
Alexander S. Klenin