RFA: fix start_subfile, start_symtab argument descriptions

["Douglas Evans" <dje@google.com>]

On the gdb list I wrote:
> 1) [...] then comp_dir should not be
> passed as the dirname argument to start_subfile in dwarf2read.c

I did some more reading and understand things better now.

Ok to check in?  This just fixes the description of the DIRNAME
argument to start_subfile and adds descriptions of the arguments to
start_symtab.

I didn't include a ChangeLog entry in this particular case since it's
just comment fixes.  I can certainly provide one if you want it
checked in with one.

Index: buildsym.c
===================================================================
RCS file: /cvs/src/src/gdb/buildsym.c,v
retrieving revision 1.55
diff -u -p -r1.55 buildsym.c
--- buildsym.c  5 Nov 2007 18:06:10 -0000       1.55
+++ buildsym.c  14 Nov 2007 21:45:45 -0000
@@ -507,7 +507,7 @@ make_blockvector (struct objfile *objfil
 /* Start recording information about source code that came from an
    included (or otherwise merged-in) source file with a different
    name.  NAME is the name of the file (cannot be NULL), DIRNAME is
-   the directory in which it resides (or NULL if not known).  */
+   the directory in which the file was compiled (or NULL if not known).  */

 void
 start_subfile (char *name, char *dirname)
@@ -778,12 +778,15 @@ compare_line_numbers (const void *ln1p,
 /* Start a new symtab for a new source file.  Called, for example,
    when a stabs symbol of type N_SO is seen, or when a DWARF
    TAG_compile_unit DIE is seen.  It indicates the start of data for
-   one original source file.  */
+   one original source file.
+
+   NAME is the name of the file (cannot be NULL).  DIRNAME is the directory in
+   which the file was compiled (or NULL if not known).  START_ADDR is the
+   lowest address of objects in the file (or 0 if not known).  */

 void
 start_symtab (char *name, char *dirname, CORE_ADDR start_addr)
 {
-
   last_source_file = name;
   last_source_start_addr = start_addr;
   file_symbols = NULL;