Work around lcc's annoying (but, even more annoyingly, legitimate)

Work around lcc's annoying (but, even more annoyingly, legitimate)
refusal to allow comparison of function pointers. Unfortunately this
still doesn't cause PuTTY to compile on my lcc installation, because
the GetCharacterPlacement stuff in exact_textout() is missing from
its header files. This may have been fixed in a future version (I'm
using lcc-win32 version 3.8 from December 2003), but I haven't
checked.

git-svn-id: http://svn.tartarus.org/sgt/putty@5527 cda61777-01e9-0310-a592-d414129be87e