[Bug preprocessor/60570] expression in 'elif' directive mis-diagnosed as error when group will be skipped

[seb.grindle at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60570

--- Comment #2 from seb.grindle at gmail dot com ---
19040 was sort of the opposite. Here we shouldn't get a error but do; there the
report was of the form "this should produce a diagostic but doesn't"