Improve documentation of gdb-mi.el

* lisp/progmodes/gdb-mi.el (gdb-show-changed-values)
(gdb-max-children): Doc fixes.

* doc/emacs/building.texi (Source Buffers, Stack Buffer)
(GDB User Interface Layout): Mention some additional
customizable variables.  (Bug#33548)

doc/emacs/building.texi

@@ -912,6 +912,7 @@ height and width values during the debugging session.
 @cindex GDB User Interface layout
 
 @vindex gdb-many-windows
+@vindex gdb-show-main
   If the variable @code{gdb-many-windows} is @code{nil} (the default),
 @kbd{M-x gdb} normally displays only the GUD interaction buffer.
 However, if the variable @code{gdb-show-main} is also non-@code{nil},
@@ -1011,6 +1012,15 @@ allows you to go backwards, which can be useful for running through
 code that has already executed, in order to examine its execution in
 more detail.
 
+@vindex gdb-mi-decode-strings
+  If the file names of the source files are shown with octal escapes,
+set the variable @code{gdb-mi-decode-strings} to the appropriate
+coding-system, most probably @code{utf-8}.  (This is @code{nil} by
+default because GDB may emit octal escapes in situations where
+decoding is undesirable, and also because the program being debugged
+might use an encoding different from the one used to encode non-ASCII
+file names on your system.)
+
 @node Breakpoints Buffer
 @subsubsection Breakpoints Buffer
 
@@ -1150,6 +1160,11 @@ also updates the Locals buffer
 (described in the next section).
 @end iftex
 
+@vindex gdb-stack-buffer-addresses
+  If you want the frame address to be shown each stack frame,
+customize the variable @code{gdb-stack-buffer-addresses} to a
+non-@code{nil} value.
+
 @node Other GDB Buffers
 @subsubsection Other GDB Buffers
 

lisp/progmodes/gdb-mi.el

@@ -1120,13 +1120,15 @@ line, and no execution takes place."
 (defcustom gdb-show-changed-values t
   "If non-nil change the face of out of scope variables and changed values.
 Out of scope variables are suppressed with `shadow' face.
-Changed values are highlighted with the face `font-lock-warning-face'."
+Changed values are highlighted with the face `font-lock-warning-face'.
+Used by Speedbar."
   :type 'boolean
   :group 'gdb
   :version "22.1")
 
 (defcustom gdb-max-children 40
-  "Maximum number of children before expansion requires confirmation."
+  "Maximum number of children before expansion requires confirmation.
+Used by Speedbar."
   :type 'integer
   :group 'gdb
   :version "22.1")