clang-format: Avoid breaking after the opening paren of function definitions

This depends on https://reviews.llvm.org/D90246 to have any effect, but once
that has landed clang-format will no longer format code like this:

int
myfunction(
    int param1, int param2, int param2)
{
   ...
}

and instead create the following:

int
myfunction(int param1, int param2,
    int param2)
{
   ...
}

Reviewed By: emaste, cem
Differential Revision: https://reviews.freebsd.org/D26978