c-lineup-arglist is a compiled Lisp function in `cc-align.el'.

(c-lineup-arglist LANGELEM)

Line up the current argument line under the first argument.

As a special case, if the indented line is inside a brace block
construct, the indentation is `c-basic-offset' only. This is intended
as a "DWIM" measure in cases like macros that contains statement
blocks, e.g.:

some (code, with + long, lines * in[it]);
<--> c-basic-offset

This is motivated partly because it's more in line with how code
blocks are handled, and partly since it approximates the behavior of
earlier CC Mode versions, which due to inaccurate analysis tended to
indent such cases this way.

Works with: arglist-cont-nonempty, arglist-close.