[Bug c/59852] Support sparse-style __attribute__((bitwise)) (type attribute)

[josh at joshtriplett dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59852

--- Comment #4 from Josh Triplett <josh at joshtriplett dot org> ---
Also note that arithmetic operations between a bitwise and a known-zero value
do not warn.

The warning on ~ of a value smaller than int only occurs if the value is not
subsequently stuffed back into the same bitwise type.  For instance, this does
not warn:

typedef unsigned short __attribute__((bitwise)) le16;

le16 i, j;

le16 k = ~i | j;