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

[joseph at codesourcery dot com]

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

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_412.htm gives an 
approved change (presumably to appear in C11 TC2) to stop #elif 
conditionals from being evaluated when they don't need to be, so it looks 
like we should in fact change this (for all standard versions, given it's 
being deemed a defect).