gdb/doc: extend the documentation for the 'handle' command

The documentation for the 'handle' command does not cover all of the
features of the command, and in one case, is just wrong.

The user can specify 'all' as signal name, the documentation implies
that this will change the behaviour of all signals, in reality, this
changes all signals except SIGINT and SIGTRAP (the signals used by
GDB).  I've updated the docs to list this limitation.

The 'handle' command also allows the user to specify multiple signals
for a single command, e.g. 'handle SIGFPE SIGILL nostop pass print',
however the documentation doesn't describe this, so I've updated the
docs to describe this feature.

Author: T-J-Teru

gdb/doc/gdb.texinfo

@@ -6760,13 +6760,14 @@ Set a catchpoint for the indicated signals.  @xref{Set Catchpoints},
 for details about this command.
 
 @kindex handle
-@item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
-Change the way @value{GDBN} handles signal @var{signal}.  The @var{signal}
-can be the number of a signal or its name (with or without the
-@samp{SIG} at the beginning); a list of signal numbers of the form
-@samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
-known signals.  Optional arguments @var{keywords}, described below,
-say what change to make.
+@item handle @var{signal} @r{[} @var{signal} @dots{} @r{]} @r{[}@var{keywords}@dots{}@r{]}
+Change the way @value{GDBN} handles each @var{signal}.  Each
+@var{signal} can be the number of a signal or its name (with or
+without the @samp{SIG} at the beginning); a list of signal numbers of
+the form @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning
+all the known signals, except @code{SIGINT} and @code{SIGTRAP}, which
+are used by @value{GDBN}.  Optional argument @var{keywords}, described
+below, say what changes to make to all of the specified signals.
 @end table
 
 @c @group