\f
/* Process the contents of include file FNAME, already open on descriptor F,
with output to OP.
- SYSTEM_HEADER_P is 1 if this file was specified using <...>.
+ SYSTEM_HEADER_P is 1 if this file resides in any one of the known
+ "system" include directories (as decided by the `is_system_include'
+ function above).
DIRPTR is the link in the dir path through which this file was found,
or 0 if the file name was absolute. */