[Bug c++/55671] -Wconversion fails to warn for sign-conversion

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55671

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-12-13 10:37:34 UTC ---
This is a common idiom in C++ and shouldn't warn e.g.

 static const size_type npos = -1;