c-ignore-auto-fill is a variable defined in `cc-vars.el'.
Its value is
(string cpp code)

*List of contexts in which automatic filling never occurs.
If Auto Fill mode is active, it will be temporarily disabled if point
is in any context on this list. It's e.g. useful to enable Auto Fill
in comments only, but not in strings or normal code. The valid
contexts are:

string -- inside a string or character literal
c -- inside a C style block comment
c++ -- inside a C++ style line comment
cpp -- inside a preprocessor directive
code -- anywhere else, i.e. in normal code

You can customize this variable.